Shearwater & JJ were made aware of this issue this week, and were able to reproduce it. It seems its an issue with the latest SOLO software, the problem only happens if the solo first time fires the solernoid after it is powered on, and the fire duration must be its minimum time (0.1 second).
A fix should be coming shortly
.
Right now, I just power down the Petrel and restart it above water if I get the warning, I haven't had a solenoid issue while diving.