Problem saving Word files

Weird problem: When saving a file in Word to one of our servers Word will lock. The file does not get saved and you must terminate Word. If you save the file locally or to any other server this does not happen. This is only happening on 3 computers running Word. It was happening on one, a file was givin to another user and then they got the problem and it started happening on a 3rd computer I used for testing. Virus? No they have been scanned with two different virus scanner. I am at a loss. It is like something in some of the Word documents “infects” Word. Help please.