Forwarded from https://launchpad.net/bugs/185311 :

"If I run Savage (a 3D non-open source game for Linux, available for download on the internet), I get loads of these messages:

silverback.bin: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) - (dpy->request)) >= 0)' failed.
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb6def767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x2e) [0xb6def81e]
#2 /usr/lib/libX11.so.6 [0xb76ca5f8]
#3 /usr/lib/libX11.so.6(XUnmapWindow+0x25) [0xb76c0fb5]
#4 libs/libSDL-1.2.so.0 [0xb7e76f01]
#5 libs/libSDL-1.2.so.0 [0xb7e7840e]
#6 libs/libSDL-1.2.so.0(SDL_VideoQuit+0x52) [0xb7e6e99a]
#7 libs/libSDL-1.2.so.0(SDL_QuitSubSystem+0x8c) [0xb7e50298]
#8 libs/libSDL-1.2.so.0(SDL_Quit+0x20) [0xb7e502ec]
#9 ./silverback.bin [0x80a95d3]
silverback.bin: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) - (dpy->request)) >= 0)' failed.
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb6def767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x2e) [0xb6def81e]
#2 /usr/lib/libX11.so.6 [0xb76ca5f8]
#3 /usr/lib/libX11.so.6(XUnmapWindow+0x25) [0xb76c0fb5]
#4 libs/libSDL-1.2.so.0 [0xb7e76f01]
#5 libs/libSDL-1.2.so.0 [0xb7e7840e]
#6 libs/libSDL-1.2.so.0(SDL_VideoQuit+0x52) [0xb7e6e99a]
#7 libs/libSDL-1.2.so.0(SDL_QuitSubSystem+0x8c) [0xb7e50298]
#8 libs/libSDL-1.2.so.0(SDL_Quit+0x20) [0xb7e502ec]
#9 ./silverback.bin [0x80a95d3]
silverback.bin: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) - (dpy->request)) >= 0)' failed.
Locking assertion failure. Backtrace:
Segmentation fault (core dumped)

I searched the web for this error, and it seems like running another 3d game, neverwinter nights, causes the same problem on Hardy.
Here's a link to that:
http://ubuntuforums.org/archive/index.php/t-666726.html
"