Two times last night, my iBook just froze and I received this error message telling me to restart the computer. After some research, I found that resetting the PMU might solve my problems. I reset the PMU per the instructions on this page at Apple.com, and the computer seems to be much faster now. More importantly, it didn’t crash at all anymore. According to the page:
“Over time, the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, not charging the battery, or not seeing the AC Adapter, among others.”