What is X Error of failed request?

[Anton Galitch]

Hi, I have just installed /usr/ports/games/flightgear, it installed fine,
but when I execute it, it shows a window starts loading, and then, craches
:S
This is what I get from the console:

%fgfs
Error reading properties:
Failed to open file
 at /home/anton/.fgfs/autosave.xml
 (reported by SimGear XML Parser)
X Error of failed request:  BadLength (poly request too large or internal
Xlib length error)
  Major opcode of failed request:  146 (GLX)
  Minor opcode of failed request:  29 ()
  Serial number of failed request:  863
  Current serial number in output stream:  863
%

I searched in google for this error, but got nothing.
Maybe you know what can produce this error.
Thanks.