Ford Fiesta Saloon Titanium 2008 - Brake warning sign - prd2808

I keep getting a warning sign showing on central information display that there is a abs brake fault when I start the car but nothing shows on the instrument panel on the dashboard.

The warning goes off as quick as it takes to read and doesn't come on again, the car has been into the local Ford garage for a full check and they cannot find anything wrong.

Also the alarm goes off at odd times for no apparant reason, therefore I am wondering if it could be caused by damp and what would be a good way of curing the problems?

Kind regards

Philip Dearle