Helicion Tech ISAPI 3 Rewrite Problem with ASP.NET 4.0, IIS6 & Extensionless URLs

For years we have used Helicon Tech’s ISAPI Rewrite plugin for IIS to generate pretty URLs for our ASP.NET sites.  A few months back I was in the process of migrating our ASP.NET web applications to the 4.0 Framework and I ran into an issue with ISAPI Rewrite and our site’s URLs.  Basically, it turned out that ISAPI Rewrite wasn’t even getting the chance to process our URL rewrites as it should.

The bottom line here is that with the 4.0 Framework and IIS 6.0, Extensionless URLs are turned on by default.  Since our rewrites were dependent on the ASPX extension to map our pretty URLs to actual pages, I had to turn this feature off.  To fix this, I had to go into the registry and find this key value:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ASP.NET\4.0.30319.0\

Then I had to add/edit this DWORD value:

EnableExtensionlessUrls = 0

I restarted IIS and ISAPI Rewrite worked like a charm.  I didn’t have this issue on my development box which runs 64-bit Windows 7 Professional and IIS 7.5.  I only had this issue on our testing and production environments which run Windows 2003 and IIS 6.0.

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