PowerShell v1 menu prompt failing

Question

When I wrote and can use the following PowerShell function under PowerShell v2 just fine. However, when I try to run it under PowerShell v1 it fails.

function Get-UserChoice
{
    param(
        [string] $Caption,
        [string] $Message = '',
        $Choices,
        [int] $DefaultChoice = -1
    );

    # Collection to hold ChoiceDescription objects
    $ChoiceCollection = New-Object System.Collections.ObjectModel.Collection``1[System.Management.Automation.Host.ChoiceDescription];

    # Create ChoiceDescription object for each choice
    foreach ($c in $Choices)
    {
        # If help text doesn't exist, set it to a blank string
        if (!($c.Help)) { $c.Help = '' }

        $ChoiceCollection.Add((New-Object System.Management.Automation.Host.ChoiceDescription($c.Label, $c.Help)));
    }

    return $Host.UI.PromptForChoice($Caption, $Message, $ChoiceCollection, $DefaultChoice);
}

PowerShell v1 error

New-Object : Cannot find type [System.Collections.ObjectModel.Collection`1[System.Management.Automation.Host.ChoiceDescription]]: make sure the assembly containing this type is loaded.
At C:\PS> ChoiceTest.ps1:11 char:35
+     $ChoiceCollection = New-Object  <<<< System.Collections.ObjectModel.Collection``1[System.Management.Automation.Host.ChoiceDescription]; You cannot call a method on a null-valued expression. At C:\MailboxMoves\ChoiceTest.ps1:19 char:30
+         $ChoiceCollection.Add( <<<< (New-Object System.Management.Automation.Host.ChoiceDescription($c.Label, $c.Help))); You cannot call a method on a null-valued expression.

I think the error being given is a red herring as I can run the following commands under PowerShell v1, and they both indicate that the Classes are available for use:

# Completes successfully and the Collection can be used
New-Object System.Collections.ObjectModel.Collection``1[System.String]

# Can't find a parameterless constructor
New-Object System.Management.Automation.Host.ChoiceDescription

What am I missing?