Files Locked or In Use ??

Interesting problem on our network. Occationally, we get a number of calls with people claiming files they try to delete gives them the message “Unable to delete. File is locked or in use by another person”. They know they are the only person using the file. We’re running Netware 5.1 and file caching is OFF. Sometimes after a couple tries of logging off/on, they are able to delete the files. We’ve also found that by rebooting the server it unlocks the files. Anyone ever encountered this?