Appletalk service getting knocked out

Weird problem with this one. we have a dual G4 with a gig of mem,running 10.28 server. we a firewire 800 card to run to lacie firewire 500gb drives. for some storage and file serving. every since then it randomly knocks out the appletalk service , knocking off all the mac clients. Does not effect the windows sharing. I can restart appletalk and it is fine for awhile. but this is causing a huge problem because files are not getting saved . any ideas?