We haven't heard any problem like this. There are two versions of NCSA Telnet 2.3, one is Telnet without MacTCP, the other is Telnet with MacTCP. Here are some things to check:
* Make sure you're using the right version of NCSA Telnet 2.3. In this case, you must use NCSA Telnet 2.3 with MacTCP.
* Was MacTCP driver installed and configured properly?
* Was Kinetics FastPath software installed and configured properly?
* Try running "MacTCP Spy" from the Macintosh OS to see if MacTCP is up and running.
* From the Sun machine, try to use "ping", a generic UNIX network utility, to send an ICMP packet to the Macintosh machine to make sure they are talking to each other.
* Try to increase the NCSA Telnet 2.3 with MacTCP application memory size. This is done via Get Info.