Odd PowerShell problem with argument transformation

I am writing a script to create a content type with two variables, a group which is selected from Managed Metadata that mimics our SharePoint Groups, and a user field.

I get the following error (note the second line which checks the type of the argument being passed):

PS C:\Users\facspqadmin> D:\PowerShell\Create-SiteColumns-and-ContentType-SingleProject.ps1
Here we have rootweb Farm Test 3 - the Submittal monster with type Microsoft.SharePoint.SPWeb
Continue (Y/N): y
y
Create-ContentType : Cannot process argument transformation on parameter 'myWeb'. Cannot convert the "System.Object[]" value of type "System.Object[]" to type "Microsoft.SharePoint.SPWeb".
At D:\PowerShell\Create-SiteColumns-and-ContentType-SingleProject.ps1:194 char:36+     $ctypeTeam = Create-ContentType($web,$ctypeParentName,$ctypeName,$ctypeGroup ...+                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ CategoryInfo          : InvalidData: (:) [Create-ContentType], ParameterBindingArgumentTransformationException+ FullyQualifiedErrorId : ParameterArgumentTransformationError,Create-ContentType

...and here is a snip of the failing code...

...which is calling the following function...

function Create-ContentType(
    [Microsoft.SharePoint.SPWeb]$myWeb,
    [string]$myParentName,
    [string]$myCtypeName,
    [string]$myCtypeGroup
)
{
    $cTypeParent = $myWeb.AvailableContentTypes[$myParentName]
    $newContentType = New-Object Microsoft.SharePoint.SPContentType($cTypeParent, $myWeb.ContentTypes, $myCtypeName)

    $newContentType.Group = $myCtypeGroup
    $myContentType = $myWeb.ContentTypes.Add($newContentType)

    return $myContentType
}

...any ideas would be most welcome. Baffled as to why it would be trying a transformation from system.object[] which means that it is not understanding the type to begin with; except it is, based on the check prior to passing the argument.