What's red flashing "S" on countax ride-on mean?

Countax C/A series garden tractor. (Fairly old abused and knackered, but still going strong despite sheer neglect!) Got a red flashing "S", or maybe a "5", on the dash below left of the hour meter. It's got an exclamation next to it so its got to be a warning! But what does it mean? The diagram on page five of the operator's manual has no related text! Can anyone help? (meanwhile I am just working my way through odds and sods like oil change.......in the hope, but I'd like to know for sure)
cheers