Hey Natasja,
Here is the thing - you are running php 5.3 . This is good
But you'll need to change few things. First of all, since this is a production server you need to turn off the error/warning/notices reporting off. That is a must! It doesn't matter what website, if it is a production site it should not show any errors connected to php to the end user.
If you do this you'll see that ccomment will most probably start to work.
The ubb/emoticon libraries that we use are not written for php5.3 - they work on it, but they are not written for it and that is why you see messages such as deprecated function etc... If you disable the error reporting you won't see those anymore.
Once you disable the error reporting try compojoomComment again. If it is still not working, then I'll again look at the site
Daniel
P.S. The next version should not generate any warnings/notices with php5.3