This problem is caused by the installation of certain other applications such as Autodesk DWG Trueview which create a conflict in mscorlib.dll.
If you have DWG Trueview installed, try uninstalling it and then re-enable MsgSave in Outlook.
If you do not have DWG Trueview installed but you do have other Autodesk applications installed, try uninstalling them one at a time until Outlook can start with MsgSave enabled. Please let us know if you find which other application is causing the problem.
If you do not wish to uninstall your Autodesk applications then please contact your Autodesk reseller.
If you do not have any Autodesk applications installed then please contact us.