Ayende @ Rahien

My name is Oren Eini
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ASP.Net WTF?! (sorry, blog was down)

time to read 3 min | 530 words

All of a sudden, I get an email telling me that my blog is down. I go and check it out, and it is indeed down. With the following error message.

Server Error in '/Blog' Application.

Could not load file or assembly 'App_Web_g5ujsn49, Version=, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.IO.FileNotFoundException: Could not load file or assembly 'App_Web_g5ujsn49, Version=, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

I tried restarting the appication by renaming web.config, but it didn't work. The only thing that worked was changing the compilation debug mode from false to true, and then to false again.

Search for the error brought this post, and it looks like there my be a hotfix avialable.  The problem is that my scenario doesn't match the conditions on the hotfix, so I really don't know what to think. I am going to ping my host and check if there is anything that can cause file locks on the server (anti virus, indexing service, etc), although I would have expect this kind of error to occur much earlier if that was the case.


Rob Eisenberg


Please post more about this if you discover anything interesting. I have seen this before, but it seemed to occur without any rhyme or reason.


see http://web-designing.inusinternational.com/Asp.net.asp


There is a bug that was fixed with the above QFE that can cause this error message to happen. What ends up triggering it is some file-system change (for example: anti-virus, a machine.config file reset, disk cleanup, etc) that causes a timing error that exposes a race condition with the compilation system.

The QFE should fix it - although we have seen a few cases where people have reported that it hasn't (what often happens is that it stops recurring once we try and look at it). We haven't completely figured out why it still fails when the QFE is applied - but if you have such a case please let us know and we'd like to debug.

As a workaround if you can't install the QFE, you can set in your web.config file. This should also avoid the error.

Hope this helps,


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