Wow, I found this:
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Skaife 05-11-2007, 03:03
Ok worked out how to fix the problem go to your computer time and adjust it to a future
date a year or so ahead should do it. Now press ok and then go back into the clock and set
it to the actual date but dont press ok. Run rfactor and when the rfactor screen comes up
now click ok on the date. It should now allow you to run rfactor at the proper date.

There is probably an easy method than that but that way worked for me.
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Holy crap, how did he find that workaround?

l8er
ronny