Need a fix on existing calendar script

I've found a bug in the calendar script: [login to view URL] and since the script is no longer updated and hasn't been for 2 years, I would like somoene to fix the problem for me. It should be a simple fix if you know what you're doing and are good with PHP. The script is very well organized from what I see. I am looking to pay $10-15 at most for this fix. The problem is that any user can login into the script by clicking "user admin". The first time they do it, they are given an "no authoritzation" warning, but if they do it again, they seem to get access. I am looking to pay $10-15 at most for this fix.