Any ideas what might be causing this problem? It seems most likely to be something about the user's configuration, but we can't seem to figure out what. Any educated guesses would be helpful.

We have a game that works fine for 99% of users, but one user is having d3d_init fail on the very first attempt to set resolution to 640x480 before the main loop even starts. Here's the relevant section of the log file:

Running {filename}.WDL.
1111 objects
D3D_Init Window: 640x480x1310356 -> 628x471 failed
D3D_Init Window: 800x600x1310356 -> Window: 1x800x600x32
Video memory found: 519 MB
Main started
Main loop..

All subsequent d3d_resize commands also fail, causing the game to run only in a window and not in full-screen mode. Nothing else fails in the acklog.

The engine is version 7.06.1 (Professional). The user runs XP Pro with SP2 and has 3GB RAM with an nVidia GeForce 6800 with 256 MB. He has the latest driver update from nVidia set to all default values. He has 2 displays, both capable of 1680x1050. One is set to its native resolution at 60 Hz. The other is set to 1280x1024 at 75 Hz.