Editing a user in Active Directory: A device attached to the system is not functioning

I'm trying to edit a user in active directory. Everything works fine and i can commit the users data except for department. When adding department I get this error:

System.DirectoryServices.DirectoryServicesCOMException (0x8007001F): A device attached to the system is not functioning.

I found the error in my C# code. I mistakenly changed another attribut that was write protected.