5
If it's XOOPS you can find the version in include/version.php. I've never used exoops, can't help you there.
Why some modules work and others don't... well, there could be hundreds of different reasons. If a module doesn't work turn on debug mode and maybe you'll get some information to explain why.
There isn't a general reason for a module not to work, it can be anything from incompatibility with the XOOPS version to server configurations and setup.