This could be one of two issues
Issue 1: Serial Cable Pin 4 problem.
Some computers will hold Pin 4 high. When this happens the Interface communications will sometimes lock up. Removing Pin 4 from the Serial cable should resolve this.
Issue 2: Hardware Issue.
With some computers there is a communications error that occurs with the INT-II. This can be fixed by adding a line to the IQ.ini file in the IQ for Windows program directory.
Using a text editor like Windows Notepad open the IQ.ini file. and in the [PORT] section add the following line.