OK, more information.
The error I'm getting when trying to use a parameter in the dynamic query used for the drop down selection:
The expression for the query ‘hardcoded_selectionquery’ contains an error: [BC30037] Character is not valid.
I can take the query parameter out and hardcode my selection list and it works. My problem may be parameter related in general as I cannot seem to figure out how to get a parameter to work at all in the dataset when it is used as input to another parameter.
Any help greatly appreciated.