At the end of a software installation, after all of the install files have been expanded to the Obsession hard drive, you will see a message displayed in the upper left corner of the screen that says "done.". At this point some Obsession II RPU's will display a message that says "Scanning for Option ROMs". As that message is displayed the processor will lock up and you will not be able to power it down from the green power switch on the front of the RPU.
This problem occurs in software versions v4.0 and higher. It is still current in v4.2.
Workaround / Fix
Unplug the power cable on the back of the RPU, wait a few seconds and then replug it. The RPU will now function properly. This bug will not corrupt the software installation that was just performed.