Getting Unknown Error on this page?.
No helpful clue in Sharepoint log or Event Viewer?
This can happen if database record in the list of published InfoPath forms had a null where it shouldn't be.
Thanks to this blog, there is small code snippet given here which will delete the culprit entry.
But make sure that you run this script under the debugger and only execute the delete operation for the offending form, otherwise it will delete all the published forms in your farm.