When making changes to one of our browser forms I came across an issue where when I would switch views in the form, I would get the generic “the form has been closed” error with no description. Checking into the server logs I found this
02/13/2009 09:08:47.20 w3wp.exe (0x1158) 0x1008 Forms Server Forms Services Runtime 82fp Warning Exception occurred during request processing. (User: server\dev, Form Name: , IP: , Request: http://server/_layouts/FormViewNotify.aspx?XmlLocation=/sites/ff/Formulations/032034.xml, Form ID: , Type: XmlException, Exception Message: There is an unclosed literal string. Line 1, position 898.)
I couldn’t find any problems in the form code or the xml schema so I hit google and found a hotfix that microsoft released for this issue. The kb is 949752 and you can get it here: http://support.microsoft.com/kb/949752. It solved my issue and the forms render fine when views are changed.