How to Add External References in Monodevelop

GTK+ adding references in MonoDevelop

Monodevelop only shows managed libraries (.net assemblies) in the references list. What you installed are native libraries which can't be directly used in gtk#.

open a .csproj with monodevelop

Create a new empty solution, copy your projects and their sources into the solution folder, then right click on the solution in the solution explorer
("View" → "Pads" → "Solution") and choose "Add" → "Add Existing Project".

MonoDevelop.AddinMaker - 'MonoDevelop.Core,5.10' is disabled

I would try deleting the addin-db-002 directory (might be called
something different) which is inside the directory of your addin's
bin/Debug directory. – Matt Ward

That was actually the problem, the addin-db-002 does not cleaned up on a Clean All, nor does it get a complete update on a Build All.

So once you have a 'corrupt' list of addin's within the sub-dir of ./addin-data/1 they do not get re-created unless you manually delete the addin-db-002.

How to skip loading a project in MonoDevelop/Visual Studio

After installing Unity 5.4.2f2 on OSX El Capitan 10.11.16 and creating and opening my first script in MonoDevelop 5.9.6 I got the same popup error:
Could not load project'Assembly-CSharp.csproj' with unknown item type '{...}'

I solved it by navigating to the following menu and enabling MonoDevelop Assembly Browser:

MonoDevelop-Unity > Add-in Manager > Installed > IDE Extensions > MonoDevelop Assembly Browser > Enable

Build MonoDevelop on Debian/Jessie using Mono 4.3.3

The solution is to download

http://github.com/directhex/xamarin-referenceassemblies-pcl

using git. Adjust the control file under debian/ directory not depending on

mono-xbuild

Build the debian package using

debuild -i -us -uc -b

then installing the package using

dpkg -i <package>

What the installation does is to copy the PCL reference assemblies to

/usr/lib/mono/xbuild-frameworks/.NETPortable.

After this compiling MonoDevelop does not show error about missing PCL reference assemblies. Hope that helps anyone trying to build latest MonoDevelop.