While DH did upgrade to PHP 5.2.2 during approximately the time period you indicated the trouble started, I think that some previous edit of your products might be more likely to be the source of the prolem.
Since you mentioned the Zen cart forums, I assume you saw this thread.
If so, what did your SQL query test show? If not, you might read through that thread and check out your product tables as suggested.
At least, that’s one place I would start.