This can happen with wrong permission or wrong path set in ubr_upload.pl

Here are some of post in uber upload forum

SourceForge.net: Uber Uploader: Developers
SourceForge.net: Uber Uploader: Developers
SourceForge.net: Uber Uploader: Developers

What type of control panel you have on server.

If your server have connection rate limiting (to protect against dos) or load balancer, uber upload will not work.