The server message is:
server is not receiving updates from client
I have added this to help others looking for help on google because at the moment a search for the above returns a massive amount of chat logs from rFactorHotlaps and similar utilities.
I noticed that at the time that people are dropped the dedicated server time starts progressing ridiculously fast, about an hour a second. This would explain the message that the server is not receiving updates from clients, because although they are sending updates, it is not quick enough for the server that is running 3600 times real time. IE The server believes 200ms has passed but in real time it is only 200ms/3600.
This problem is described as an issue with certain dual core processors and older Windows operating systems when combined with the +fullproc switch in the rFactor Dedicated server. We were using Windows Server 2008 R2 SP1 with the +fullproc switch and having the above message happen at random times.
Fix 1 = add a /usepmtimer switch to boot.ini. Unfortunately Server 2008 no longer has a Boot.ini and the BCD system that it uses doesn't appear to recognise the usepmtimer command.
Fix 2 = Don't use the +fullproc switch. This is the method we are testing at the moment.
As the problem seems to happen intermittently there really is no way to prove that either of these fixes works apart from running the server over time and seeing if it happens again. Will report findings after a reasonable period of time... real time, not x 3600.
Cheers all