Thanks to Prof who pointed out this is another addon track where race distances are all messed up. As a result I had a quick play with changing the track's GDB file to allow for sensible race distances.
There are two solutions, download
http://www.avonrise.co.uk/gtr/Norisring.gdb (
right click, save target as) and overwrite the existing file in gtrgamedir\gamedata\locations\norisring
Alternatively edit the file Norisring.gdb in the above directory and change the
RaceLaps line to
RaceLaps = 200Doing either of these will stop loads of GDB mismatch errors being generated when people join the server