If this issue only started showing up recently, I strongly suggest using System Restore to return your PC to a time where the game was running smoothly, then disabling automatic Windows driver updates.

I feel 100% positive at this point that it's a combination of something changed by the 4.01 patch coupled with something Windows related that's causing the error, because I was having the exact same issue where I started getting crashes at progressively greater frequencies until I couldn't even log in consistently and resolved it by restoring my PC to a point prior to a particular Windows update.