Running WebDAV code against Windows 2008(IIS7) and getting HTTP Error 404.11?

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I ran into this same issue and then discovered the following KB:

Error message when you visit a Web site that is hosted on IIS 7.0: "HTTP Error 404.11 – URL_DOUBLE_ESCAPED"
https://support.microsoft.com/kb/942076

Setting the allowDoubleEscaping="true" did resolve my problem but this approach slightly compromises the server security by leaving it open to “Double Encoding” attacks.

The cause of the problem was the “+” sign in the name of some of the .eml files. In fact any file that has a “+” in the file name + is hosted on IIS7 + does not have the allowDoubleEscaping set to true will give you the HTTP Error 404.11.

IIS7 rejecting URLs containing +
https://blogs.iis.net/thomad/archive/2007/12/17/iis7-rejecting-urls-containing.aspx