mono xbuild fail error : Error building target GetReferenceAssemblyPaths: UNC paths should be of the form \\server\share

Question

I have a solution which I can build without any issue. However my co-worker gets the following error:

error : Error building target GetReferenceAssemblyPaths: UNC paths should be of the form \\server\share

We both have the same version of mono installed. What else in the our environments could be causing the issue?

Here is the output on my machine:

XBuild Engine Version 14.0
Mono, Version 4.6.1.0
Copyright (C) 2005-2013 Various Mono authors

Build started 01/02/2017 12:32:33.
__________________________________________________
Project "E:\path\WindToolsService.sln" (Rebuild target(s)):
    Target ValidateSolutionConfiguration:
        Building solution configuration "Debug|Any CPU".
    Target Rebuild:
        Project "E:\path\myproject\myproject.csproj" (Rebuild target(s)):
            Target CoreClean:
                Deleting file 'E:\path\myproject\obj\Debug\.NETPortable,Version=v4.5,Profile=Profile78.AssemblyAttribute.cs'
                Deleting file 'E:\path\myproject\obj\Debug\myproject.dll'
                Deleting file 'E:\path\myproject\bin\Debug\myproject.dll.mdb'
                Deleting file 'E:\path\myproject\bin\Debug\myproject.dll'
                Deleting file 'E:\path\myproject\bin\Debug\protobuf-net.dll'
                Deleting file 'E:\path\myproject\obj\Debug\myproject.dll.mdb'
                Deleting file 'E:\path\myproject\obj\Debug\myproject.csproj.FilesWrittenAbsolute.txt'
            Target PrepareForBuild:
                Configuration: Debug Platform: AnyCPU
            Target CopyFilesMarkedCopyLocal:
                Copying file from 'E:\path\packages\protobuf-portable-net.2.0.0.668\lib\portable-net45+wp8+win8\protobuf-net.dll' to 'E:\path\myproject\bin\Debug\protobuf-net.dll'
            Target GenerateSatelliteAssemblies:
            No input files were specified for target GenerateSatelliteAssemblies, skipping.
            Target CoreCompile:
                Tool C:\Program Files (x86)\Mono\bin\mcs.bat execution started with arguments: /noconfig /debug:full /debug+ /optimize- /out:obj\Debug\myproject.dll IMessage.cs IMessageCallbackLookup.cs IMessageLookup.cs IMessagePubSub.cs Message.cs MessageCallbackLookup.cs MessageCallbacks.cs MessageLookup.cs MessageLookupFactory.cs Properties\AssemblyInfo.cs TestMessages.cs obj\Debug\.NETPortable,Version=v4.5,Profile=Profile78.AssemblyAttribute.cs /target:library /define:"DEBUG;TRACE" /nostdlib /reference:..\packages\protobuf-portable-net.2.0.0.668\lib\portable-net45+wp8+win8\protobuf-net.dll /reference:"C:\Program Files (x86)\Mono\lib\mono\xbuild-frameworks\.NETPortable\v4.5\Profile\Profile78\\mscorlib.dll" /reference:"C:\Program Files (.......

Here is the output on the failing machine:

XBuild Engine Version 14.0
Mono, Version 4.6.1.0
Copyright (C) 2005-2013 Various Mono authors

Build started 01/02/2017 14:46:49.
__________________________________________________
Project "C:\path\WindToolsService.sln" (Rebuild target(s)):
        Target ValidateSolutionConfiguration:
                Building solution configuration "Debug|Any CPU".
        Target Rebuild:
                Project "C:\path\myproject\myproject.csproj" (Rebuild target(s)):
                        Target PrepareForBuild:
                                Configuration: Debug Platform: AnyCPU
: error : Error building target GetReferenceAssemblyPaths: UNC paths should be of the form \\server\share.
                Done building project "C:\path\myproject\myproject.csproj".-- FAILED
                Project "C:\path\Portable.Reprogramming\Portable.Reprogramming.csproj" (Rebuild target(s)):
                        Target PrepareForBuild:
                                Configuration: Debug Platform: AnyCPU