The info you provide seem too few for us to be able to help you (but I may be wrong). Reading the docs for Net::Telnet, I see that there is a Debugging section which suggests to enable input_log and debug_log - did you try them? What was the result?

Moreover, you should check the result of your open call here. From the docs:

Time-outs don't work for this method on machines that don't implement SIGALRM - most notably MS-Windows machines. For those machines, an error is returned when the system reaches its own time-out while trying to connect.

If your open does not succeed, you keep going with the login method, but the server is likely to have closed the TCP connection, and Net::Telnet gets an EOF back when reading from the socket.