Error initializing task: Not registered task

Question

I am trying to build an orignally-Windows/VisualStudio C# project on my mac. Specifically, I am trying to convert this chatterbot API to a dll so I can use it in my own C# files.

$ xbuild ChatterBotAPI.csproj

But I get all these errors:

XBuild Engine Version 14.0
Mono, Version 4.4.2.0
Copyright (C) 2005-2013 Various Mono authors

Build started 20/12/2016 14:00:55.
__________________________________________________
:  warning : Default tasks file /Library/Frameworks/Mono.framework/Versions/4.4.2/lib/mono/3.5/Microsoft.Common.tasks not found, ignoring.
Project "~/Documents/Programming/chatter-bot-api/dotnet/ChatterBotAPI/ChatterBotAPI.csproj" (default target(s)):
    Target PrepareForBuild:
: error : Error initializing task Message: Not registered task Message.
            Target _RecordCleanFile:
: error : Error initializing task ReadLinesFromFile: Not registered task ReadLinesFromFile.
                Build FAILED.
                Warnings:
                :  warning : Default tasks file /Library/Frameworks/Mono.framework/Versions/4.4.2/lib/mono/3.5/Microsoft.Common.tasks not found, ignoring.
                Errors:
                ~/Documents/Programming/chatter-bot-api/dotnet/ChatterBotAPI/ChatterBotAPI.csproj (default targets) ->
                /Library/Frameworks/Mono.framework/Versions/4.4.2/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets (PrepareForBuild target) ->
                    : error : Error initializing task Message: Not registered task Message.
                ~/Documents/Programming/chatter-bot-api/dotnet/ChatterBotAPI/ChatterBotAPI.csproj (default targets) ->
                /Library/Frameworks/Mono.framework/Versions/4.4.2/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets (PrepareForBuild target) ->
                (_RecordCleanFile target) ->
                    : error : Error initializing task ReadLinesFromFile: Not registered task ReadLinesFromFile.
                     1 Warning(s)
                     2 Error(s)
                Time Elapsed 00:00:00.1460680

How do I get all these classes into some sort of library that I can use in other programs?