Had a very similar problem with our server.Our IT department had reset & disabled our permisions.We would open folders older than a day old and then once you alter them and go to save, a similar message would appear.Couldnt delete the files either.It was if they were read only documents, but their properties said they werent.Is this problem related to only particular files?What if you create a new file and save it to your hard drive?That should bypass the server and youll start to know where to look.