Well, after installing Lansweeper on another server, the results have led me to believe that Microsoft ISA 2004 is somehow blocking the necessary functions from working. I would have tried the MS patch that you mentioned, but the clients that have problems are both XP PCs (at both SP2 and SP3) and Server 2003 servers. That patch doesn't work on servers, so I decided to install Lansweeper on a different server and it works flawlessly.