I'm afraid I don't know anything about your errors.
But in answer to reforming a .XSN:
When you're inside IP you can "Extract Form Files..." ("File" menu) to export all files separately, where you can then edit/overwrite them. Conversely, if you have a working manifest.xsf, you can edit that in IP, and when you save you then get a .XSN file. Finally, a .XSN is just a .CAB file with a different extension, you can get at the files if it will not read into IP by renaming to .CAB and then a CAB tool/WinZip/Explorer will be able to extract the individual files.
Like Greg says, changing one file can be tricky, as contents of other files may need to reflect the changes before it's acceptable to IP. But at least maybe you have a starting point for rescuing your stuff. Use the techniques above to get at individual files. Either start with your bad files and play till they seem to work or show you where the error is, or start with a new working IP file and incorporate in your bad files till you find what goes wrong...