I have been using SelfSSL tool from The IIS Resource Kit to test ASP.NET HTTPS connectivity for some time now, but suddenly the connection refused to work. Checking IIS settings (ports, certificates etc.) showed that everything was A-OK. And yet pages were not displayed. And then a beautiful utility came to the rescue.

Running SSL Diagnostics revealed following:

And sure enough, SSPIFILT.DLL was missing from ISAPI filters. Not sure how it happened, but adding it back solved the problem (small correction though: I had to add it at “Web Sites” group level, adding it at Web Site level for some reason didn’t work).

You can download SSL Diagnostics by istself or as a part of IIS Diagnostics toolkit. 64-bit versions also available.