I have a Lenovo/IBM ThinkPad T60 at work with a docking station. For the longest time, I'd get this error when trying to undock:
You cannot eject your computer because one of the devices in the docking station, "Printer Port (LPT1)," cannot be stopped because a program is still accessing it.
For the life of me, I couldn't figure out what the problem was. I don't have any printers hooked up, I hadn't printed anything, I couldn't find anything that was using the port.
There's a KB article on it, and I found forum posts about it, but no real solutions. The way I solved it:
In the BIOS at boot time, there is an option for disallowing access to the printer port from the docking station. I set that. (There is an option to disable the printer port entirely, but I didn't need to do that - I just needed to stop the docking station from accessing it.) A quick save and reboot, and I'm ready to eject from the docking station at any time - no more error.
Note that I don't have any printers locally attached to my machine, so disabling the printer port connection to the docking station didn't hurt me. If you have a local printer attached to your docking station, this may not be the best solution for you.
UPDATE: I am on ThinkPad T60 BIOS version 2.21 and the option is under Config -> Docking Station. Set the "Legacy Devices on Mini Dock" setting to "Disabled" to disallow the docking station access to the parallel port.