I had the same problem with an MRC Superbrain 969 Charger. The button contacts are most likely dirty.
Mine was out of warranty so this is what I did:
I disassembled the unit,
Sprayed the affected areas (buttons) with a good quality electric motor cleaner,
Used low power compressed air to 'flash off' the cleaner,
This worked until I sold it 6 months later, I haven't heard of the buttons going bad again from the guy who bought it, over a year now.
Be sure that you make sure that all of the spray cleaner is evaporated and dried before you energize the unit.