Did you see my post this morning, in response to
@xoSx.Racing? You can see it
here if not. The long and short of it is that I think the server package for this event may have been conflicting with an existing package for the GT3 race at Zolder that took place earlier this year. Anybody who took part in that event, and/or still has the (old) package installed (or maybe has some remnants hanging around) from joining that server, would probably have experienced this issue. I suspect that uninstalling the old package before installing the new package was therefore enough to rectify the problem.
That being said, I have now created an entirely new version of the server package to hopefully avoid any further occurrences of this problem. Can you please confirm that you are now able to join the server successfully, without having to manually install the new server package?