Has anyone had any problem at with their ASR/ESP system at all. Just that on a couple of occassions when attempting a hill start mine has switched itself off & I wasn't able to turn it back on.

Yep, everyone on here probably

Any idea what causes it & how to solve it.

Cause is probably over-sensitive FIAT electrics/sensors.

Nothing to worry about as long as it goes off next time the car starts, OR if it remains on constantly. Then it may need to go onto Examiner.

No doubt one of the FIAT tech boys will be on soon.

Cheers!