http://bugs.winehq.org/show_bug.cgi?id=30203
--- Comment #4 from Henri Verbeet hverbeet@gmail.com 2012-03-18 10:37:13 CDT --- (In reply to comment #2)
This is an assertion in nouveau driver, so you have to try to update it or use proprietary one.
To add to that, the backtrace is missing function names and line numbers, but this is probably the assert in get_rt_format() in nv10_state_fb.c. It gets triggered because during wined3d startup we try to attach a GL_RGB5_A1 texture (among various others) to an FBO. The driver should probably fail the FBO completeness test for formats it doesn't know how to handle instead of asserting.