Here are some techniques to try when you are having trouble getting 4D Client connected to 4D Server (e.g. -10002 errors):

Try using another networking protocol. If TCP doesn't work, maybe ADSP (AppleTalk) or IPX will; in that case you know the physical network is up but that one protocol is misconfigured.
Try connecting from a computer on the same hub or switch with the 4D Server to rule out wider network configuration problems. If practical, isolate a small segment of your network with just the server and 1 client then expand until the problem occurs.
For TCP, Try entering the IP address of the server into the "More choices..." section of the 4D Client open connection dialog (indicated with the mailbox flag on Macintosh). If this works but you can't see the 4D Server listed in the initial dialog, then 4D Server's broadcasts are being blocked between the subnets that the server and client reside on.
For TCP, check basic connectivity with a PING utility. For ADSP, try setting up File Sharing and connecting via AppleShare. This will help determine if it is a 4D problem or general network problem.
For TCP, make sure the subnet mask and router address are correct for each machine. For ADSP, make sure your Zones (if any) are properly configured.
Remove the TCP.OPT, ADSP.OPT or IPX.OPT file from the active Windows directory in the 4D folder (ACI folder for 6.5.x) or from the System Folder:Preferences on Macintosh. These files are used to customize the application port number for 4D Server.