Error: Cairo 1.4.14 does not yet support the requested image format:
        Depth: 16
        Alpha mask: 0x00000000
        Red   mask: 0x00007c00
        Green mask: 0x000003e0
        Blue  mask: 0x0000001f
Please file an enhancement request (quoting the above) at:
http://bugs.freedesktop.org/enter_bug.cgi?product=cairo
gaim: cairo-image-surface.c:199: _cairo_format_from_pixman_format: Assertion `NOT_REACHED' failed.
Abort


This message showed up for a user using a Citrix terminal server.   He had configured Citrix for a "16-bit" display, but in this case, it apparently uses only 5 bits for each color.  He was able to work around the problem by selecting 
a "24 bit" display, but he prefers 16-bit for "work at home" due to the improved performance.


If it helps, I was able to reproduce the problem using a VNC server started with:

  vncserver -depth 15 -pixelformat RGB555

(I understand that this is an unusual VNC configuration, and it's easy to use something else.   This is just for testing, and simulating the Citrix case.  It's apparently not possible for the Citrix users to select an alternative format)