I updated my Nvidia drivers (I have 8800 GTS 640MB) to the very latest. Anyway, I can get rFactor to boot up normally, but it won't load any maps/tracks. Here is the error message I get:

Error opening MAS file COMMON MAPS.MAS

What to do? rFactor ran fine with ancient drivers but I'd rather not go back to them.

Did you run the rF Config.exe after you changed drivers?
You can get a new CommonMaps.mas file here:
ISI rF files.
That's the original for 1.255.
If you need another version, go to the main page and select the version you need.
Good luck

I forget all the ways to get that error, but one way it happens may involve trying to use a mod in All Tracks & Vehicles that isn't compatible with it.
(I'd try to narrow it down... I'd guess it's the car mod causing it if no track will load.)

By itself, I don't think updating video drivers would cause a commonmaps.mas error.

I haven't installed a new car mod, so that can't be it. I did download and install some new tracks.

UPDATE: tried the "common mas" file - thank you very much - it works with some tracks but not others. Even the tracks it works for I experienced weird anomalies making racing impossible. I guess I'm done with rFactor. I have no idea what happened. One of the tracks that I donwloaed from the rFactor site somehow destroyed the common.mas files in every installed track. Crap.

Well, before you give up rFactor for good I'd advise you to give it another try by reinstalling it from scratch at first. Backup the old installation though first, if possible on a different disk drive.

Then - after having installed it - backup the user data and copy the old user data from the old installation to the freshly reinstalled version.

Then add mods as you see fit. Try it - I was there where you are now, but admittedly I had the advantage of running three different installations of rFactor. Thus I didn't have to begin from scratch.

But where do I put the CommonMaps.mas file? I tried inserting into each track. That didn't work.

In \GameData\Locations under your main rFactor install folder.

Thank you, Smithee! That did it! Everything is working now. Wonderful!

A great way to avoid trouble like this, and simplify mod installation/uninstallation in general, is to use Jonesoft Generic Mod Enabler.

Thanks for the tip!