@PRJIM - just took delivery of my Roadster #1438 yesterday, and after some rain this morning and the car being parked outside, I plugged my UMC in, and experienced this error as well. I.D. 286. and 288.
I previously had the same issue with my 2.5 #1213 when it got snowed on. From my knowledge, it appears to be a safety mechanism that disconnects electrical current through the vehicle when it feels threatened by moisture. What I still DON'T understand, however, is WHEN it decides it's okay to restart.
It does worry me that this car already shows this issue when it rains. I washed the car yesterday when I got it with zero issues, too.
Very strange.
UPDATE: according to the Wiki, ID 288 is the following.
288: BSM: V_ess too low during precharge, t2.
Anyone have experience with this, and can elaborate?