Well for starters, no setting should break your DFP. If it happened, they would be obligated to send you a free one as there is no warning about it happpening. As far as I know, just mess arund until you get what works best for you. I don't know if you tried searching or not... but do try if you didn't. Mods frown upon hordes of the same threads hogging bandwidth.
Oh and hey dantran. Shut up as your post was worse than his. You wasted space when his post was an honest question. Even if the thread is a bit impulsive...
Anybody who is more intelligent than I, or at least owns a DFP, can tell him right. (booooy)