We have similar problem. We have enabled editing Mirosoft Office files in the Alfresco 6.1 CE. When user opens Word file with Microsoft Office the file is open in read-only mode. We tried allowing Alfresco server as trusted location without success. At the same time other users on the network open and edit Microsoft Office files without any problem.
In this forum I could not find any clues or more or less adequate solutions so far.