I'm sure that the Freeware F units "work" but they cause my system to barf with a fatal Train Simulator and an offer to send the info to Microsoft (right :)

They also cause the Activity Editor to barf whenever I try to work with a consist in which they appear.

Meanwhile, conbuilder doesn't find anything wrong with them.

I wonder if there are any suggestions.

It sounds as though your video card can't handle large textures. The F uses 1024 x 1024 images, which may be a problem for Voodoo and older cards. You can convert and resize the included A1_Main.ace and B1_Main.ace files to 512 x 512. If you're not familiar with the process let me know and I'll upload an update.

Cheers!
Marc