.NET Runtime version 2.0.50727.42 - Fatal Execution Engine Error (7C812AEB) (800703e9)

This error will not allow you to open VS 2005 IDE. All that will happen is you 'll see the VS2005 splash screen and then "puff" devenv.exe vanishes, and no trace of it in process manager too.

When I saw it for the first time, I lost my cool. I dinlt know what was happening and itr took me one full night to diagnose the problem and identify solution. But I have to acknowledge that it was fun doing that

First and foremost, be a developer and own the problem. Solution can come only when you know what the problem is. Seaching in google at this point won't help will not help as you don'w know what the problem is

Here are tips to identify the problem
1. Clear all the logs in Event Viewer (Application, Security, System). Control Panel -> Adminiutrative tools ->Event Viewer
2. Open Visual Studio
3. If it fails to open, check the log messages in Application, security and System section of event viewer

Now that you know the error, you can hunt for it in google/MSDN/Microsoft's website
If the error you see in the system is

".NET Runtime version 2.0.50727.42 - Fatal Execution Engine Error (7C812AEB) (800703e9)"
Here are somethings that you can try to resolve it
1. uninstall the .NET Framework 2.0 security hot"fix" 922770.
Check if VS 2005 is alright - If yes, you are all set
2. Uninstall Visual Studio 2005 Extensions for Windows Workflow Foundation
Check if VS 2005 is alright - If yes, you are all set
3. Reinstall Visual Studio 2005 Extensions for Windows Workflow Foundation
Check if VS 2005 is alright - If yes, you are all set