New Post: A parameter cannot be found that matches parameter name 'eq'.

Alright. I reverted the script back to its original form. which included the following:

Show-InstallationPrompt -Message "The installation of $appName $appVersion complete." -ButtonRightText 'OK' -Icon Information -NoWait

and continues to display the following

The installation of $appName $appVersion complete.

but, not before trying your recommendation which failed to display the "installation prompt" all together.

Show-InstallationPrompt -Message 'The installation of '$appName' '$appVersion' complete.' -ButtonRightText 'OK' -Icon Information -NoWait

In addition to the oddities noted above the script completely ignores what I assumed to be simple and sound branching logic.

While I understand that

' vs "

can adversely affect the execution of the script; in a side be side comparison of the script below and a script that I slightly modified (the one containing the single quotes) and the differences were negligible. I am thoroughly confused as to why PSADT 3.1.4 equivalent of the problematic PSADT 3.5.0 script below executes flawlessly. Please help me understand where my oversight lies.

<#
.SYNOPSIS
    This script performs the installation or uninstallation of an application(s).
.DESCRIPTION
    The script is provided as a template to perform an install or uninstall of an application(s). 
    The script either performs an "Install" deployment type or an "Uninstall" deployment type.
    The install deployment type is broken down into 3 main sections/phases: Pre-Install, Install, and Post-Install.
    The script dot-sources the AppDeployToolkitMain.ps1 script which contains the logic and functions required to install or uninstall an application.
.PARAMETER DeploymentType
    The type of deployment to perform. Default is: Install.
.PARAMETER DeployMode
    Specifies whether the installation should be run in Interactive, Silent, or NonInteractive mode. Default is: Interactive. Options: Interactive = Shows dialogs, Silent = No dialogs, NonInteractive = Very silent, i.e. no blocking apps. NonInteractive mode is automatically set if it is detected that the process is not user interactive.
.PARAMETER AllowRebootPassThru
    Allows the 3010 return code (requires restart) to be passed back to the parent process (e.g. SCCM) if detected from an installation. If 3010 is passed back to SCCM, a reboot prompt will be triggered.
.PARAMETER TerminalServerMode
    Changes to "user install mode" and back to "user execute mode" for installing/uninstalling applications for Remote Destkop Session Hosts/Citrix servers.
.EXAMPLE
    Deploy-Application.ps1
.EXAMPLE
    Deploy-Application.ps1 -DeployMode 'Silent'
.EXAMPLE
    Deploy-Application.ps1 -AllowRebootPassThru -AllowDefer
.EXAMPLE
    Deploy-Application.ps1 -DeploymentType Uninstall
.NOTES
.LINK 
    http://psappdeploytoolkit.codeplex.com
#>
[CmdletBinding()]
Param (
    [Parameter(Mandatory=$false)]
    [ValidateSet('Install','Uninstall')] 
    [string]$DeploymentType = 'Install',
    [Parameter(Mandatory=$false)]
    [ValidateSet('Interactive','Silent','NonInteractive')]
    [string]$DeployMode = 'Interactive',
    [Parameter(Mandatory=$false)]
    [switch]$AllowRebootPassThru = $false,
    [Parameter(Mandatory=$false)]
    [switch]$TerminalServerMode = $false
)

Try {
    ## Set the script execution policy for this process
    Try { Set-ExecutionPolicy -ExecutionPolicy 'ByPass' -Scope 'Process' -Force -ErrorAction 'Stop' } Catch {}
    
    ##*===============================================
    ##* VARIABLE DECLARATION
    ##*===============================================
    ## Variables: Application
    [string]$appVendor = ''
    [string]$appName = 'Wireshark'
    [string]$appVersion = '1.12.3'
    [string]$appArch = ''
    [string]$appLang = 'EN'
    [string]$appRevision = '01'
    [string]$appScriptVersion = '1.0.1502.11'
    [string]$appScriptDate = '2015.02.11'
    [string]$appScriptAuthor = 'alexayr'
    ##*===============================================
    
    ##* Do not modify section below
    #region DoNotModify
    
    ## Variables: Exit Code
    [int32]$mainExitCode = 0
    
    ## Variables: Script
    [string]$deployAppScriptFriendlyName = 'Deploy Application'
    [version]$deployAppScriptVersion = [version]'3.5.0'
    [string]$deployAppScriptDate = '11/17/2014'
    [hashtable]$deployAppScriptParameters = $psBoundParameters
    
    ## Variables: Environment
    [string]$scriptDirectory = Split-Path -Path $MyInvocation.MyCommand.Definition -Parent
    
    ## Dot source the required App Deploy Toolkit Functions
    Try {
        [string]$moduleAppDeployToolkitMain = "$scriptDirectory\AppDeployToolkit\AppDeployToolkitMain.ps1"
        If (-not (Test-Path -Path $moduleAppDeployToolkitMain -PathType Leaf)) { Throw "Module does not exist at the specified location [$moduleAppDeployToolkitMain]." }
        . $moduleAppDeployToolkitMain
    }
    Catch {
        [int32]$mainExitCode = 1
        Write-Output "Module [$moduleAppDeployToolkitMain] failed to load: `n$($_.Exception.Message) `n$($_.InvocationInfo.PositionMessage)"
        Exit $mainExitCode
    }
    
    ## Handle ServiceUI Invocation
    If ($serviceUIExitCode) { Exit-Script -ExitCode $serviceUIExitCode }
    
    #endregion
    ##* Do not modify section above
    ##*===============================================
    ##* END VARIABLE DECLARATION
    ##*===============================================
        
    If ($DeploymentType -ine 'Uninstall') {
        ##*===============================================
        ##* PRE-INSTALLATION
        ##*===============================================
        [string]$installPhase = 'Pre-Installation'
        
        #CheckExist modified to include Application version
        if (((Get-InstalledApplication -Name "Wireshark 1.12.3 (64-bit)") -eq $appName) -and ($appDisplayVersion -eq $appVersion)) {
        
            Show-InstallationPrompt -Message "An installation of $appName $appVersion exists." -ButtonRightText "Ok" -Icon Information -NoWait; Write-Log "ErrorCode Return value is: 1638, proceeding."; Exit-Script -ExitCode 1638
        } else {
        
            # Show Welcome Message, close Internet Explorer if required, allow up to 3 deferrals, verify there is enough disk space to complete the install and persist the prompt
            Show-InstallationWelcome -CloseApps "wireshark,op_flse,aceanalyst" -AllowDefer -DeferTimes 5 -CheckDiskSpace -PersistPrompt
        
            # Show Progress Message (with the default message)
            Show-InstallationProgress
            }
        
        ##*===============================================
        ##* INSTALLATION 
        ##*===============================================
        [string]$installPhase = 'Installation'
        
        ## <Perform Installation tasks here>
        if ($is64Bit -eq $true) {
        Execute-Process -FilePath "Wireshark-win64-1.12.3.exe" -Arguments "/S /desktopicon=no /quicklaunchicon=no" -WindowStyle Hidden -IgnoreExitCodes "1,2,3"
        } Else {
        Execute-Process -FilePath "Wireshark-win32-1.12.3.exe" -Arguments "/S /desktopicon=no /quicklaunchicon=no" -WindowStyle Hidden -IgnoreExitCodes "1,2,3"
        }
        
        
        ##*===============================================
        ##* POST-INSTALLATION
        ##*===============================================
        [string]$installPhase = 'Post-Installation'

        ## <Perform Post-Installation tasks here>

        ## Display a message at the end of the install
        Show-InstallationPrompt -Message 'The installation of $appName $appVersion complete.' -ButtonRightText 'OK' -Icon Information -NoWait
    }
    ElseIf ($DeploymentType -ieq 'Uninstall')
    {
        ##*===============================================
        ##* PRE-UNINSTALLATION
        ##*===============================================
        [string]$installPhase = 'Pre-Uninstallation'
        
        #CheckExist modified to include Application version
        if (((Get-InstalledApplication -Name "Wireshark 1.12.3 (64-bit)") -eq $appName) -and ($appDisplayVersion -eq $appVersion))  {
    
        # Show Welcome Message, close Internet Explorer if required with a 60 second countdown before automatically closing
        Show-InstallationWelcome -CloseApps "wireshark,op_flse,aceanalyst" -CloseAppsCountdown "60"
    
        # Show Progress Message (with the default message)
        Show-InstallationProgress
                    
        ##*===============================================
        ##* UNINSTALLATION
        ##*===============================================
        [string]$installPhase = 'Uninstallation'
        
        # <Perform Uninstallation tasks here>
        if ($is64Bit -eq $true) {
            Execute-Process -FilePath "$envProgramFiles\Wireshark\uninstall.exe" -Arguments "/S" -WindowStyle Hidden -IgnoreExitCodes "1,2,3"
            } Else {
            Execute-Process -FilePath "$envProgramFilesX86\Wireshark\uninstall.exe" -Arguments "/S" -WindowStyle Hidden -IgnoreExitCodes "1,2,3"
            }
        
            # Display a message at the end of the uninstall
            Show-InstallationPrompt -Message "The uninstallation of $appName $appVersion complete." -ButtonRightText "Ok" -Icon Information -NoWait     
        } else {
        
            Show-InstallationPrompt -Message "$appName $appVersion is not installed." -ButtonRightText "Ok" -Icon Information -NoWait; Write-Log "ErrorCode Return value is: 1605, proceeding."; Exit-Script -ExitCode 1605
            }
        
        
        ##*===============================================
        ##* POST-UNINSTALLATION
        ##*===============================================
        [string]$installPhase = 'Post-Uninstallation'
        
        ## <Perform Post-Uninstallation tasks here>
    }
    
    ##*===============================================
    ##* END SCRIPT BODY
    ##*===============================================
    
    ## Call the Exit-Script function to perform final cleanup operations
    Exit-Script -ExitCode $mainExitCode
}
Catch {
    [int32]$mainExitCode = 1
    [string]$mainErrorMessage = "$(Resolve-Error)"
    Write-Log -Message $mainErrorMessage -Severity 3 -Source $deployAppScriptFriendlyName
    Show-DialogBox -Text $mainErrorMessage -Icon 'Stop'
    Exit-Script -ExitCode $mainExitCode
}