Rights and Permissions changing

We recently installed a new NWSB 5.1. Ever since being installed we have ocassional file save errors. It says the we don’t have rights or permission to save the file. Even when logged in as admin. I have had it happen to regular users also. I would have to go back into NWADMIN and redo the rights and permissions to a share. It would be okay for a day or two and then it would do it again. It seems to happen primarily to Word 2000 files. Any ideas?

Brian