I have an issue... I was printing perfectly with some filament from www.filamentsupply.com. Every day I had to increase the temperature by about 5C to get the results I had the day before. Then after about a week of steady consistent printing. The stuff just plain stopped working.

I am convinced that this is a filament quality issue, as I switched to the filament that came with the printer and I have perfect prints again.

My question is whether the plastic can be revived and secondly how can I prevent this in the future?

Plastic doesen't "go bad" as food might, although it might have absorbed some moisture. That shouldn't affect adhesion tho as it boils off in the extruder. Often different brands of fillament have different properties. One brand may stick well to plain glass, while another may need hairspray or lemon juice. My usual testing order is as follows:

Plain Glass
Hairs sprayed glass
3M blue tape
3M blue tape with ABS juice
3M blue tape wiped down with acetone then wiped with ABS juice

I hope something works, as there's nothing more disappointing than having an unusable roll of fillament.