Open Amp Sensor error in GD compressor

Hi

I am working on Gardner Denver Compressor model Electra Saver.
I recently came across an error message Shutdown 'Open Amp Sensor'

This error message popped up within few minutes upon turning on. There is a light on the Compressor motor as seen in above pic, don't know what it means. The motor doesn't get hot.

After pressing Reset & then Constant run, the compressor runs, in most of the cases - all day. But sometimes it stops after running for few hours with above error message.

I tried to look thru the manual but couldn't find above Error message.
Any thoughts what this error is for & how to fix it?

Thanks