Error passing query parameter to Opportunity form

We are getting a generic "An error has occured." message when trying to pass a query parameter to read optimized opportunity form. If we remove the parameter from the URL or if we add rof=false to the URL, form loads fine.

Works: main.aspx?etn=opportunity&pagetype=entityrecord&extraqs=param_name%3dtest&rof=false

Error: main.aspx?etn=opportunity&pagetype=entityrecord&extraqs=param_name%3dtest

The setup is CRM Online with UR12.

Any help is greatly appreciated.