Cathedral disappears in TGE 1.5.1

I exported the cathedral and placed it in the barebones mission for testing.
When I look at it from certain angles it disappears, and reappears from another angle!
If I go inside, in certain locations it disappears, when I go back it reappears.

Does it only with the cathedral, simple objects render fine.

I am running a Laptop with an older card ATI M7 (Mobility) 64MB.