Have you tried connecting to the server with a new calendar file on that machine? That would give some insight as to the nature of the problem. If a new file connects okay to the server, it means there's likely a problem with either the data file, or the server settings for that particular file.

Are you connected to the server via static IP address, or using Bonjour?

Can you ping the server from the client machine that's having the problems using the network utility or the ping command from the terminal?
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Sean Boiarski
Product Manager, Now Software