[MonoDevelop] Unable to start MonoDevelop after upgrade to Ubuntu 8.04

[Gino Heusdens]

When I try to run monodevelop after upgrading to Ubuntu 8.04 I get the 
following error:

    WARNING: Cannot find Mozilla directory containing libgtkembedmoz.so.
    Some Addins may not be able to function. Please set
    MOZILLA_FIVE_HOME to your Mozilla directory.

    ** (./MonoDevelop.exe:29874): WARNING **: The class
    Mono.Addins.Localization.IAddinLocalizer could not be loaded, used
    in Mono.Addins, Version=0.3.0.0, Culture=neutral,
    PublicKeyToken=0738eb9f132ed756

    Unhandled Exception: System.TypeLoadException: Could not load type
    'Mono.Addins.Localization.IAddinLocalizer' from assembly
    'Mono.Addins, Version=0.3.0.0, Culture=neutral,
    PublicKeyToken=0738eb9f132ed756'.
      at MonoDevelop.Startup.SharpDevelopMain.Main (System.String[]
    args) [0x00000]

I tried to reinstall the mono addins without succes. I also checked the 
Global Assembly Cache for the mono addin assembly and i looks like the 
right version is installed.

    gino at gino-laptop:~$ gacutil -l Mono.Addins
    The following assemblies are installed into the GAC:
    Mono.Addins, Version=0.3.0.0, Culture=neutral,
    PublicKeyToken=0738eb9f132ed756
    Number of items = 1

Can someone point me in the right direction so I can fix this problem?