I searched the forum and found some suggestions but none is working.
So i installed both version into their own folders and also reinstalled them with administrator rights.
I also deleted the MonoDevelop folder before installing.
So now i can not change a script with MonoDevelop.
Can anyone help or have other suggestions?
It is on Windows 7 64bit.
So i searched more in the forum and found something that did not help me but maybe would help others.
You can try to delete the Monodevelop 4 Folder in the path Users/(user)/AppData/Roaming/MonoDevelop-Unity-4.0.
This helped some users but not me.
The new thing today is that i got a MonoDevelop error that i can read the first time. Here it is:
System.IO.IOException: Die Datei ist vorhanden.
bei System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
bei System.IO.__Error.WinIOError()
bei System.IO.Path.InternalGetTempFileName(Boolean checkHost)
bei System.IO.Path.GetTempFileName()
bei MonoDevelop.Components.CairoExtensions.LoadImage(Assembly assembly, String resource) in c:\BuildAgent\work\5c6d706b6ad8bc12\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components\CairoExtensions.cs:Zeile 544.
bei MonoDevelop.Components.MainToolbar.LazyImage.get_Img() in c:\BuildAgent\work\5c6d706b6ad8bc12\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:Zeile 45.
bei MonoDevelop.Components.MainToolbar.LazyImage.op_Implicit(LazyImage lazy) in c:\BuildAgent\work\5c6d706b6ad8bc12\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:Zeile 57.
bei MonoDevelop.Components.MainToolbar.RoundButton.GetIcon() in c:\BuildAgent\work\5c6d706b6ad8bc12\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:Zeile 159.
bei MonoDevelop.Components.MainToolbar.RoundButton.OnExposeEvent(EventExpose evnt) in c:\BuildAgent\work\5c6d706b6ad8bc12\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:Zeile 181.
bei Gtk.Widget.exposeevent_cb(IntPtr widget, IntPtr evnt)
I am not sure that this is something with Unity or the MonoDevelop Window?
Again i just started a new project, created a csharp script and this time also use the name that unity give it and after that try to open it. When i click on send or do not send MonoDevelop exit.
Oh, just forget to mention that i installed Unity and MonoDevelop not on C: but on D:.
I read somewhere that it should be on C but it worked for me the last years and hopefully will do it again.
Edit:
Just to be sure i installed it now on C: but get the same crash. This time again without an error.
Edit2:
I can also not start MonoDevelop alone to chande the adons i.e. deselect the boo language like i read also somewhere that helped someone.
Please help, i can not work on scripts now.
I am sorry to bump but i can not work with unity now.
I need help please.
I read something about gtk#
Could that be the problem?
Can i installe MonoDevelop (i.e. 5.0.1) from xamarin and use it with Unity or is the unity one a special kind of MonoDevelop?
Edit:
Tried to install the xamarin version but that do not install because gtk# is not installed on my machiene in the number at least 2.2 or so.
Tried to download the latest gtk# for win7 64bit but there is no installer only something to change with a path wich i have done but can not install xamarin still.
This is so frustrating. I can not work and do not know why it suddenly stopped to work after all the yeas without a problem.
These might help?
Windows MonoDevelop Required packages:
.NET Framework 4.0 Download
GTK# for .NET 2.12.26 Download
Thank you gruddlebug, i installed them, restarted the pc but it does not work.
But at least someone tried to help me 
I hope Unity can help here.
Unity can usually only help if you submit a bug report…
Sorry for the necro post but hoping this can help anyone who hits this page from a search engine.
I just had a similar error and after a lot of uninstalling and reinstalling libraries I tracked it down to my c:\Temp folder possibly containing too many files. I did a disk cleanup (including system files for good measure) and Monodevelop started working again. Incidently I had nearly 2GB of temporary files so that may be an indicator if you have the same problem.
The error in English is:
System.IO.IOException: The file exists.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.__Error.WinIOError()
at System.IO.Path.InternalGetTempFileName(Boolean checkHost)
at System.IO.Path.GetTempFileName()
at MonoDevelop.Components.CairoExtensions.LoadImage(Assembly assembly, String resource) in c:\buildslave\monodevelop\build\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components\CairoExtensions.cs:line 544
at MonoDevelop.Components.MainToolbar.LazyImage.get_Img() in c:\buildslave\monodevelop\build\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:line 45
at MonoDevelop.Components.MainToolbar.RoundButton.OnSizeRequested(Requisition& requisition) in c:\buildslave\monodevelop\build\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Components.MainToolbar\RoundButton.cs:line 148
at Gtk.Widget.sizerequested_cb(IntPtr widget, IntPtr requisition)