What I'm wondering is if you connect directly to the serial port, and if so, what TCP port you're using.
Here are examples of connecting to port 1 directly with telnet, first with ASCII telnet, then with a binary telnet connection:
ASCII telnet: telnet <ip of PSII> 2001
Binary telnet: telnet <ip of PSII> 2101
If you haven't tried both those methods, I'd recommend trying them and compare your results. Might be that one will work and the other won't, etc.
Also, the port needs to be configured as device type "prn" to allow a connection to it. Here is an example of setting port 1 to this dev type:
set ports range=1 dev=prn
You'll also need to make sure that flow control (set flow range=1) and line parameters (set line range=1) on the Portserver II match whatever is connected to that serial port as well. To configure more than one port, a wildcard (*) can be used for all ports, or a range (ex. 1-16) can be specified for whichever ports you want to configure in this manner.