Hi John,
I reproduced your issue, and I found a workaround.
You need to manually change the XML configuration for the catalog. Change the type for the Guid parameter from "System.Data.SqlDbType.UniqueIdentifier" to "System.Data.SqlDbType.NVarChar".
Once you do that the conversion from a String to a Guid will be done in the ADO.Net layer instead of within the QuickApps code.
The only thing that you need to watch out for is if you try to edit that operation in ezEdit again, your configuration will get lost because the Type parameter will not be what it expects and you'll need to set it up again.
Bill