I am really bad to assist in this type of things because I don't know much about this. But I looked on many forums and threads in internet if there could be a solution to this problem. And I found out that many people who had problems to run the MP game just like Kern, but there weren't the same 'error advert'. There were errors which emerged from problems in relation with ATI videocards for older games like this one. Still some people who have problems with jk3 files just like Kern, fixed this by following the steps on the pages, even though it didn't seem to have connection with the ATI videocards's case.
I am really not a book for this things as I said, so probably I am guiding you away of the real solution to something else that doesn't have nexus with. But if the information on the links helps you, at least it won't be useless for fixing the problem.