KDE 4.3 Fails to Load after System Update (Solution)

After installing my system updates yesterday, KDE 4.3 failed to load upon reboot this morning. It boots until it reaches the KDE login screen (with KDM) but it will let me log in from there at all.

The last updates installed were:

• Package: xserver-common, version 2:1.6.4-2ubuntu4.1
• Package: xserver-xorg-core, version 2:1.6.4-2ubuntu4.1

Though I suspect that the recent updates to gcc/g++ and libc/libstdc++ may have also affected this. I can't be sure.

Either way, I don't know exactly what the problem was, but here is the solution I found. My '.Xauthority' file in my home directory was the problem. I don't know what was wrong with it, but after I cleared that file of all contents, KDM let me log in normally. I hope this fix works for anyone else.