In more recent versions of OFP, especially version 1.91 and above, this may be caused by memory management problems. Take a look at this FAQ item to see if any of the steps there might help you resolve this problem, even if you're not seeing any of the error messages mentioned there.
even if you're using the latest and/or most stable drivers for your graphics card, this has been know to occur. Several players solved this problem by going into their PC's BIOS program and lowering their AGP aperture size from 256MB to 64MB, for example. For some players, that wasn't enough. They had to also disable their BIOS program's AGP fast write option to finally resolve this problem.
If you're using an ATI Radeon 8500 graphics adapter, this might be caused by OFP version 1.30's and later version's W-BUFFER setting being enabled.
Now normal folks could click on OPTIONS on OFP's main menu to get to the W-BUFFER setting and disable it but you can't (ha-ha-ha).
Have no fear! OFP player pAth0s solved this problem manually by editing file USERINFO.CFG in the following path from within OFP's base directory: \users\player_name\ . Change player_name to the actual player name you use in OFP. In file USERINFO.CFG, change the following line:
Save and restart OFP.