Error in console log I can't find googling, iPad crashing - help!

My iPad has been unstable for a few weeks, I had been explaining it by thinking I'd let my Exchange inbox/calendar get out of hand, but when I started looking at the consold log in iPCU when troubleshooting, I saw a lot of these errors:

Tue Mar 1 07:18:19 iPad kernel[0] <Debug>: AppleAD7147A::readProxData delta is lower than negative tolerance (-67)
Tue Mar 1 07:18:19 iPad kernel[0] <Debug>: AppleAD7147A::readProxData _sensorDataFailures exceeded allowed limit (50)

Literally dozens of them in a row, hadn't ever seen them before and I can't find them anywhere online, which worries me. Can anyone shed any light on this?

Thanks,
Guy