There could be a number of causes:
- Maybe you need to restart the node on server 1 after adding the rpcallowip line to its configuration.
- Maybe you have the wrong port number for the rpcport (don't confuse with the p2p port).
- Maybe there is a software firewall on server 1 preventing incoming connections on the RPC port.
Note also that for an individual IP address in rpcallowip you can just include that IP address without the /255.255.255.255 suffix.