Breaking ASP.NET 4.0 Framework on Windows 7 and IIS 7.5 with ASP.NET 1.1 Framework

The other day, I wanted to migrate some database changes from our development environment to our staging servers. The tool we typically use to do this is kind of old and requires the ASP.NET 1.1 Framework. So, during the installation of the tool on my new Windows 7 box, I saw a message requiring the 1.1 framework and decided to install it. During its installation, a warning popped up about known compatibility issues on my system, but I decided to proceed anyway. I mean, how bad could it be?

Well, it turned out kind of bad. None of my ASP.NET 4.0 web applications on my development box would run. I kept getting an error in the framework itself:

Calling LoadLibraryEx on ISAPI filter “C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_filter.dll” failed

Apparently you can’t run the 1.1 Framework alongside the 4.0 Framework, at least not on Windows 7.  It might work fine on XP or Windows 2003 Server, but I’m not 100% sure and I wasn’t going to waste too much time figuring out if you could or not.

To make a long story short, I had to install all of the ASP.NET Frameworks from my development box and re-install the 2.0 and 4.0 Frameworks and then make sure they were registered by running aspnet_regiis -r in the installation directory for each Framework version.  It took me about half a day of beating my head against my desk to figure out this faux pas.  Better to listen to the warning messages next time…

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