From: Leeuwarden, Netherlands
Exactly what 82nd says, check your production. It *is* possible that your PP tab says 100+ production, but it's quite possible that that is only one or more PP production lines that "build up" because they can't "deliver" their PP's to their designated HQ. Sometimes the map is too big, or your opponent has cut your lines, to deliver your produced PP's to their designated HQ's.
To circumvent this problem, and this counts also for other things produced and not delivered, create a new HQ in that city, and set that city to produce it's PP's (or whatever you're producing there) to that new HQ. Heck, the new HQ doesn't even need staff! Just an empty HQ unit suffices. The PP's created there go directly into the PP pool. Not so with newly produced Inf/tanks/planes, *they* go to that newly created HQ, but I'd rather have that than a huge build up that never arrives at your SHQ. Don't forget, you'll lose that production line / PP buildup when your opponent takes that city.
Hope that helps kick some butt LOL