I was constructing a webpage with an InfoPath form and a QueryFilter webpart on it. After saving it i coudn’t open the new page from a browser. It threw a correlation error at me.
Using the ULSviewer i traced down to this errormessage: hidden property cannot be set on web part [web part name] since it is a standalone web part.
The reason i got this error was that i placed the QueryFilter webpart outside of a webpartzone on the page. Moving it into a webpartzone (i first had to create one) solved my problem.