gnome-panel crashing on a vncserver startup

[Crusty]

Whenever I login to this box and startup a vncserver or tightvncserver manually gnome-panel crashes with the following error.

gnome-panel: /build/buildd/libcairo-1.4.2******/cairo-image-surface.c:199: _cairo_format_from_pixman_format: Assertion `NOT_REACHED' failed.
Error: Cairo 1.4.2 does not yet support the requested image format:
Depth: 8
Alpha mask: 0x00000000
Red mask: 0x00000007
Green mask: 0x00000038
Blue mask: 0x000000c0
Please file an enhancement request (quoting the above) at:
http://bugs.freedesktop.org/enter_bug.cgi?product=cairo
nautilus: /build/buildd/libcairo-1.4.2******/cairo-image-surface.c:199: _cairo_format_from_pixman_format: Assertion `NOT_REACHED' failed.

Because of this, nothing else seems to startup for the gnome session, not even nautilus. I changed the xstartup file to add an xterm to see if it was vnc causing the problems.. but that opens up just fine.. of course with no window manager or gnome-panel to go with it.

This is on a freshly updated Ubuntu Feisty.

Any ideas?

edit: I've done the usual of removing all the .gnome .gnome2 .gconf .metacity config files as well, and this happens with all users on the system.