I'm using mono 4.2 from the alpha channel.
When compiling https://github.com/grokys/Perspex/ (commit 845b28a2c2ce858786bb11e1aa413916b2bb061d) in monodevelop I get the error:
'CS1591' is not a valid warning number (CS1904)
Fixed in master and next 4.2 alpha
This appears to still be a problem in 4.2.2:
targets (CoreCompile target) ->
CSC: error CS1904: `CS1591' is not a valid warning number
This fix is still only available in master and Mono 4.3.2 previews
I'm currently experiencing the same thing with an up-to-date version of Xamarin and the latest version of Mono (4.6.2).
Is there any way to resolve this?