It's a bit tricky, but this isn't necessarily a bug at all. According to D&D rules, a cleric can use divine spells from scrolls that are of a spell level that he can currently cast. That is, a 5th level cleric can cast 3rd level spells, and thus any scroll with a t 3rd level or lower spell should be no problem.
You must also have the relevant ability score high enough. For a sixth level cleric spell, you must have a 16 or higher wisdom. Even if you do, then when the spell is of a higher level than you can cast on your own, even after identifying them, which is required, there's no guarantee if the spell level is too high. You have to succeed on a caster level check. If you fail that, you may suffer an unfortunate mishap.
See
Scrolls :: d20srd.org
But the easiest solution to your problem is to use the heal potion that is located in the same location you got the scroll. Anybody in your party can use that on Bing, and he'll be fine.