I upgraded my development machine to 64-bit Win7, and now when I try to connect to a local ASP.Net project I get:

HTTP Error 500 ... Calling LoadLibraryEx on ISAPI filter "C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_filter.dll" failed

There are several puzzling things about this; the ASP.Net project was a .Net 2.0 ASMX so it was using C:\Windows\Microsoft.NET\Framework\v2.0.50727. If it updated to x64 without asking me, should it not use C:\Windows\Microsoft.NET\Framework64\v2.0.50727\? Where is C:\Windows\Microsoft.NET\Framework\v4.0.30319\ coming from?

I opened IIS Manager and the selected .Net Framework version for my machine is 2.0.50727. Framework version for my default application pool is the same.

I am developing in VS2008, which does not even have an option for targeting .Net 4.0.

2 Answers 2


It sounds to me like you have a 32 bit part of your application, and your trying to run it in a 64bit application pool in IIS. By default the application pool is 64bit on a 64bit OS. To enable 32bit mode you need to go to the advanced properties of the application pool and change the setting for "Enable 32 Bit Applications".

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  • Good idea, but enabling 32-bit has no effect. The app is supposed to be 64-bit-safe. Even debug statements in the global.asax are not output. Jan 28, 2011 at 23:18

Despite the fact the .Net 2.0 Framework was installed on my machine, and selected in IIS Manager, ASPNET_REGIIS said it was not registered:

cd C:\Windows\Microsoft.NET\Framework\v2.0.50727

aspnet_regiis -lv
    4.0.30319.0 C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll
    4.0.30319.0 C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll

How this is possible I do not know. Re-registering ASP.NET 2 fixed the problem:

aspnet_regiis -i
    Finished installing ASP.NET (2.0.50727)

aspnet_regiis -lv
    2.0.50727.0 C:\Windows\Microsoft.NET\Framework64\v2.0.50727\aspnet_isapi.dll
    4.0.30319.0 C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll
    2.0.50727.0 C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll
    4.0.30319.0 C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll

It had nothing to do with upgrading to Win 7; that was a wild-goose chase.

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