Comment 18 for bug 284505

Marcus: Try removing "fglrx, 8.543, 2.6.24-21-generic, x86_64: installed (original_module exists)" if you get the 'Saw signal 11' error in your Xorg log. It appears (perhaps) to be the conflict between the module built for the old kernel that causes the module for the new kernel to fail.

Alejandro: As for reinstalling the vboxdrv driver - setup (/etc/init.d/vboxdrv setup) failed for me with a compile error that's also been seen in some versions of fglrx (although I don't have the references to hand, something about too many parameters on one file), which is what also led me to removing the modules compiled for previous kernels from dkms.

It seems, from the previous couple of entries, that it is the 'installed' status of modules for previous kernels that causes the problem. Maarcus' fails because his 2.6.24 is 'installed', but alejandro's works because it's just 'built' not 'installed'. Of course this also means that you can't revert to the old 2.6.24 kernel without backing out of these module changes, and definitely points to a conflict in the way different kernel versions of modules are handled by 2.6.27.