Moving to El Capitan? Then you need Mono version 4.2.x or 18.104.22.168.
From the Mono mailing list:
What is the difference between the latest Mono 22.214.171.124 package for Mac and the 4.2.1 El Capitan Preview? The changelog of 126.96.36.199 includes “33585: El Capitan System Integrity Protection support.” so i suppose that the 188.8.131.52 also works on El Capitan?.
Reply from Miguel de Icaza:
One is based on Mono 4.0 series, with minimal changes just to enable the support on El Capitan; The 4.2 has the same changes, on top of the latest Mono 4.2, available on Alpha and the release candidate.