The following discussion assumes all troubleshooting such as clean boot, trying to print from DOS, etc. has yielded negative results.
Printing does not interact with the expansion bus in any way. I suspect the problem is in the type of parallel port being used. Some computers are equipped with what is commonly referred to as a bi-directional or EPP parallel port. We have seen problems with these type of ports due to the non-standard pinout of these ports.
Sometimes it is possible to make the printer work by using a different cable with these ports - not all cables have all pins connected and by disconnecting some of the non-standard pins the printer can be made to work. This is a somewhat hit and miss proposition, so it is usually better to get another parallel port (since you can buy one for less than 20 dollars, it's a cost effective solution)
Some bi-directional or EPP ports have an option to turn off that functionality. Check the documentation to determine if that's an option.
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