Mono 2.11 with nginx or apache
The install package is placing some files in the wrong place. For Apache, you'll have to move the file mod-mono-server4.exe from /usr/lib/mono/4.0 to /usr/lib/mono/4.5 and update the reference inside the file /usr/bin/mod-mono-server4.
If you were using XSP or FastCgi, the same treatment would be required for xsp4.exe and fastcgi-mono-server4.exe and their respective references in /usr/bin.
(I am starting to regret I followed down this Mono path... )