IIS and 403.1 Error

Today I was tormented by the following error from IIS:
HTTP 403.1 Forbidden: Execute Access Forbidden

I checked the directory security permissions in Windows, gave everyone under the sun god-like permissions on the whole folder tree, checked anonymous authentication, checked the server logs … but still this error came.

It turns out it was because I had “.com” in the folder name – something it would have taken a couple of months to figure out without Google:
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