Can't start Omnisharp because of mono version

Question

Whenever I start up VS Code on my Mac (Yosemite), I get the following error in VS Code

Error: Cannot start Omnisharp because Mono version >=3.10.0 is required

<

Answer 1

I had the same problem. In /Library/Frameworks/Mono.Framework/Versions I had three different mono versions 2.10.9, 3.12.1 and 4.0.0 with 4.0.0 being the 'Current'.

Yet the mono version on my command line path was 2.10.9.

$ which mono
/opt/local/bin/mono

For me the fix was to remove the mono version I had installed ages ago in Macports (the bin files for Macports are stored in /opt/local/bin).

$ sudo port uninstall mono
--->  Deactivating mono @2.10.9_0
--->  Cleaning mono
--->  Uninstalling mono @2.10.9_0
--->  Cleaning mono

After doing that new and 'Current' mono from /usr/bin/mono on my Mac was picked up and Visual Studio Code could load my sln files and use Omnisharp - yay :)

$ mono --version 
Mono JIT compiler version 4.0.0 ((detached/d136b79 Mon Apr 13 14:40:59 EDT 2015)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
    TLS:           normal
    SIGSEGV:       altstack
    Notification:  kqueue
    Architecture:  x86
    Disabled:      none
    Misc:          softdebug 
    LLVM:          yes(3.6.0svn-mono-(detached/a173357)
    GC:            sgen