Close the database on FMP 11 Server.
Copy the database to one of the client machines. Open. Save As Smaller.
Open smaller save database on client with IWP enabled and test that?
This may help to diagnose the problem as a database problem, server problem or browser cache issue.
Try it .. Still getting the bad URL messages from the IWP users.. all browser versions. And I cleared the cahce files from the web broswers before trying..