Get-PWDocumentsBySearch Documents Not Found

I have encountered a problem with the Get-PWDocumentsBySearch Cmdlet.

The code is:  $docs = Get-PWDocumentsBySearch -FolderPath $Document_Path -GetAttributes {$ -eq "Test Document%"}

The PowerShell transcript reports the following errors:

PS H:\> TerminatingError(Get-PWDocumentsBySearch): "Illegal characters in path."
Get-PWDocumentsBySearch : Illegal characters in path.

You cannot call a method on a null-valued expression.

I have checked the obvious points such as variable values, search path. The path is defined as a text string with quotaion marks (" ").

In this example there are two documents which meet the path and name criteria.

Any support would be appeciated.