HTTP Error 404.11 - Not Found
The request filtering module is configured to deny a request that contains a double escape sequence.
The request contained a double escape sequence and request filtering is configured on the Web server to deny double escape sequences.
Details of the issue is available at:
Resolution summary: Would suggest to read the complete article but just for quick reference I am typing the resolution here.
%windir%\system32\inetsrv\appcmd set config "Default Web Site" -section:system.webServer/security/requestfiltering - allowDoubleEscaping="true"
Or change manually by opening the following file
%windir%\System32\inetsrv\config\applicationHost.config file in notepade. (remember to open notepade with administrator privilege.
and change following value.