It’s Arduino Uno, not Mega.
I’ve not seen that before - when I originally wrote the remote configuration, it would compile with no errors. I’ll need to look into this.
(It would be a lot easier for me if you could copy a screen grab rather than posting an image.)
[edit]
The emonTx V3.4 sketch released alongside the software for the emonPiCM The emonPiCM compiles perfectly for me. This leads me to suspect that your problem was introduced when Trystan made the Low Power Labs version.
[/edit]
I can’t answer this - the Raspberry Pi website is surely the place to look. I suspect it will depend on which model of Pi you have.