If you have a file comparison program, such as WinDiff (available as part of MSDN), then you can create a new form that works, and extract both forms out to individual files and do a file comparison. You can do this without an extra program but its a much more tedious process.
The most likely culprit will be the manifest.xsf, but it could also be in the template.xml, sampledata.xml, or any of the view .xsl files. Honestly it could be any of them, but I'd start with the files I mentioned in the order I mentioned them.
The first thing is to get another form created with save working to do the comparison with.
Greg Collins [InfoPath MVP]