I had this problem a couple times during that level range as well. Universally, it was because either people were taking too much avoidable damage, or the DPS was having issues.

It was not always their fault - I synced to 32 for Braflox two days ago, and ran out of mana because our DPS were both casters and had to run around too much to dps efficiently.

Once you get SoS, your mana problems disappear.