Comment 1 for bug 1541950

In addition:

build@hindlet:~$ monodevelop --no-redirect
INFO [2016-02-02 18:33:57Z]: Starting MonoDevelop 5.5
INFO [2016-02-02 18:33:57Z]: Running on Mono 4.2.1 (Debian 4.2.1.102+dfsg2-5ubuntu1)
INFO [2016-02-02 18:33:57Z]: Did not find previous version from which to migrate data
INFO [2016-02-02 18:33:57Z]: Using GTK+ 2.24.29
ERROR [2016-02-02 18:33:57Z]: MonoDevelop failed to start. Some of the assemblies required to run MonoDevelop (for example gtk-sharp)may not be properly installed in the GAC.
System.Exception: Toolkit could not be loaded ---> System.IO.FileNotFoundException: Could not load file or assembly 'Mono.Cairo, Version=4.0.0.0, Culture=neutral, PublicKeyToken=0738eb9f132ed756' or one of its dependencies.
File name: 'Mono.Cairo, Version=4.0.0.0, Culture=neutral, PublicKeyToken=0738eb9f132ed756'
  at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) <0xf59ae730 + 0x000a3> in <filename unknown>:0
  at System.RuntimeType.CreateInstanceMono (Boolean nonPublic) <0xf57dfc60 + 0x00149> in <filename unknown>:0
  at System.RuntimeType.CreateInstanceSlow (Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, System.Threading.StackCrawlMark& stackMark) <0xf57dfc00 + 0x00048> in <filename unknown>:0
  at System.RuntimeType.CreateInstanceDefaultCtor (Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, System.Threading.StackCrawlMark& stackMark) <0xf57df980 + 0x00056> in <filename unknown>:0
  at System.Activator.CreateInstance (System.Type type, Boolean nonPublic) <0xf56e0330 + 0x0009f> in <filename unknown>:0
  at System.Activator.CreateInstance (System.Type type) <0xf56e01c0 + 0x00025> in <filename unknown>:0
  at Xwt.Backends.ToolkitEngineBackend.CreateBackend (System.Type backendType) <0xf46fe688 + 0x0005f> in <filename unknown>:0
  at Xwt.Backends.ToolkitEngineBackend.CreateBackend[T] () <0xf46fe628 + 0x00023> in <filename unknown>:0
  at Xwt.Toolkit.Initialize (Boolean isGuest) <0xf46fd4b8 + 0x000f3> in <filename unknown>:0
  at Xwt.Toolkit.LoadBackend (System.String type, Boolean isGuest, Boolean throwIfFails) <0xf46fd0d8 + 0x00127> in <filename unknown>:0
  --- End of inner exception stack trace ---
  at Xwt.Toolkit.LoadBackend (System.String type, Boolean isGuest, Boolean throwIfFails) <0xf46fd0d8 + 0x001a3> in <filename unknown>:0
  at Xwt.Toolkit.Load (System.String fullTypeName, Boolean isGuest) <0xf46fccc8 + 0x00077> in <filename unknown>:0
  at Xwt.Application.Initialize (System.String backendType) <0xf46fcbf0 + 0x00027> in <filename unknown>:0
  at Xwt.Application.Initialize (ToolkitType type) <0xf46fc728 + 0x0001b> in <filename unknown>:0
  at Xwt.Application.InitializeAsGuest (ToolkitType type) <0xf46fc6e0 + 0x00013> in <filename unknown>:0
  at MonoDevelop.Ide.IdeStartup.Run (MonoDevelop.Ide.MonoDevelopOptions options) <0xf46f3118 + 0x00573> in <filename unknown>:0
  at MonoDevelop.Ide.IdeStartup.Main (System.String[] args, MonoDevelop.Ide.Extensions.IdeCustomizer customizer) <0xf749e030 + 0x00167> in <filename unknown>:0

find /usr/lib/mono -name Mono.Cairo*
/usr/lib/mono/4.5/Mono.Cairo.dll
/usr/lib/mono/gac/Mono.Cairo
/usr/lib/mono/gac/Mono.Cairo/4.0.0.0__0738eb9f132ed756/Mono.Cairo.dll
/usr/lib/mono/gac/Mono.Cairo/4.0.0.0__0738eb9f132ed756/Mono.Cairo.dll.config

Which I solved by:

Setting MONO_PATH so that it can find Mono.Cairo.dll allow monodevelop to start.

MONO_PATH=/usr/lib/mono/4.5/ monodevelop --no-redirect