Telnet control is not working?

This issue is typically releated to the use of the "Use Telnet Encoding":

"Most" devices do not require this option.

Use Telnet Encoding: When checked, the client connection will be established using negotiation as specified by the Telnet protocol. When unchecked, it will not attempt to negotiate (raw TCP). Keep this box unchecked unless your device specifically requires true Telnet. This does not apply to the server mode.