I found the answer to my problem buried in a thread somewhere, but it was only alluded to.
If you run a server with Jailbreak installed, whether or not you're running a Jailbreak game currently, you can get Invalid Package errors when a client connects if the versions don't match.
I had downloaded "jailbreak2004-zip.zip" for my server, and the client had downloaded "jailbreak2004a-zip.zip." Whatever is in the change, I assume, made UT's internal cheat protection kick in.
EDIT: Like I said this can be found somewhere on this forums alluded to, but maybe not if you don't know to search for Jailbreak as the culprit.
You always get file mismatches if the packages of server and clients are named the same but differ in size.
It's a problem not exclusively with Jailbreak.
I really recommend you update your Jailbreak installation to jailbreak2004a or Jailbreak Service Pack 1 as it's commonly referred to.
Be sure to follow these instructions if you do:
I know you will have problems with any package. I was posting because Jailbreak will be a more common package that is installed. Therefore, I was posting for the casual server admin, such as myself.
thanks for heads-up..:up: