Just wanted to document this. On boot I got the following on a nextstation color turbo:
Testing FPU, SCC, SCSI, Enet, RTC
System test failed: error code 91
The system would continue to boot, however would hang on shutdown.
Searching the old newsgroups brought up the following description:
Real-Time Clock Tests
Error Code Meaning
91 RTC didn't tick after 0.3 seconds.
In my case it turned out that the battery connection needed to be reflowed.