Gosh, "premature end of headers" is making me nightmares
But... make sure ubb_upload.cgi is uploaded to your UBB's cgi-bin directory; make sure it's chmodded to 755; make sure that "vars_config.cgi" is also in that directory, if not, change ubb_upload.cgi line 23 to its place; make sure vars_modifications.cgi is chmodded to 777; make sure you CHANGED modification settings and used a CORRECT path for uploads, a directory that already exists and that is chmodded to 777; no more ideas