My 6500 just threw the above error while I was away doing something totally unrelated. Neither normal power down/up nor factory reset would clear it. Unplugged the power for 5 mins and the fault went away.
Gerald previously posted "The message says that your 1V power supply is running low at 0.92V. When the voltage goes below 0.92V, the supervisory processor will shut down the CPU and reports that error. " but his examples used a power threshold of 0.92V.
If it returns, especially if you are certain the radio's external power didn't vary or drop you might put a Help Ticket in.