How do you get around this problem? Currently Unity won't even start up; when Unity starts to load up the error pops up and Unity crashes. Cannot even startup Unity at all- complete show stopper. There is little to no information on the Unity forums on this error, eventhough there are other developers that have run into the same issue.
Suggestions? Workarounds? Is there a patch?
System: Win 7 64-bit Nvidia GeForce 8800 GT DirectX 11.0
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Hi, uninstall Kaspersky cause this error 
I did it and installed Avira and now it works perfectly
The problem has been solved; here is some information that may help anyone that may come across this problem in the future:
this error does not occur with Kaspersky 2010 running Win 7 32-bit
this error only occurred for us running machines with Win 7 64-bit and Kaspersky 2010
we fixed it by:
1) uninstall Kaspersky 2010 from Win 7 64-bit machine 2) install Unity 3.0 (test it, should work) 3) install Kaspersky 2011 (latest version) after making sure that Unity 3.0 is working 4) now everything should work fine
Again, problem is found to only affect Win7 64-bit machines. I think there should be a note of this on the Unity 3.0 official release notes; would save others a lot of time and headache.
I would just like to add that this bug still exists in Unity 3.1 (downloaded from the main web site literally today) and I do NOT have Kaspersky installed, and never have had.
It worked the very first time I ran Unity, but trying to open it again beyond that causes the error shown above. It's totally un-usable.
Did you try the search? This question has already been asked and answered: Fatal error in gc: GetThreadContext failed (?)
This error also exists when using the ESET Smart Security (NOD32) suite.
Nice Game Engine .... Terrible piece of Software ....
DKZ
Try preferences → show project wizard at startup. Brings up the project window and you have to choose the project every time, but it seemed to get around it on mine :). I had this happening alot.
I’ve got the solution. Just set the program compatibility mode to Vista(Service Pack 2) in Windows 7 x64 Operating System.
Solution : disable your network card , start unity , enable the network card(tested on 4 PC multiple times with 100% success rate)
It seems that the solution [for Unity 4] is here : GetThreadContext failed solution
The problem still exist in 4.6f3 with Windows 8.1 x64, here I’m using Windows Defender.
Adding Unity.exe or the entire path ""C:\Program Files (x86)\Unity\Editor" it to the excluded path didin’t solve the problem.