Dogs that are stressed out or overstimulated may not take treats. (During classes, if we sit too near his 'girlfriend', my 10 month old collie will politely take treats from me when offered them, and spit them out- usually in her direction. :P) Is he giving you any calming signals like yawning, looking at you then looking away, lip-licking, etc? If that's the case, he may be stressed out or overstimulated, rather than hungry. (And with good treats like cheese, I'd bet on mildly stressed, before I'd guess not hungry.) Spend this week getting him onto a feeding schedule, rather than free-feeding, find some REALLY stinky treats this week (like freeze dried liver, Natural Balance rolls, or baked/dehydrated sliced liver) and see if that works.

(Freeze dried liver, so you know what it looks like)
Additionally, some dogs find play more rewarding than food, especially in high stress situations. Does he like to pounce on a squeaky toy and kill it? Most terriers do, and that can work as a reward, too.
HTH,
Cait