Share randomly gives permission error

I had reports of this from users, but didn't really believe them until it just happened to me. I had a share from my 10.4.9 Xserve mounted on my 10.4 client. Been working on it all morning. Then, all of a sudden, the share goes to a Folder with the red minus symbol thing. I was in Firefox at the time, not doing anything on the server. Also, I had another share also from the Xserve mounted, and that one was still accessible. The fix was just to eject both and reconnect. This has happened to multiple people on both Macs and PCs (XP) over the last week or so. Any ideas?