Like magic, the program opened without the error. He slowly moved the plug-ins back in, one by one, until he found the culprit: a damaged booklet-building file. He replaced it with a fresh copy from his old install CD, and the error vanished into the digital ether.
If rebuilding preferences fails, a specific plug-in may be the culprit: Go to the plugins folder in the PageMaker directory. Locate the "pic" plug-in file. adobe pagemaker plugin error 7212