A Land Far Away

I've just made a priestly NPC that casts healing spells and when testing instead of casting the spell she "jitters" about chasing the PC. If you can get away from her she casts the spell, but it's a bit weird. I'm using the standard conversation action script "cast spell at object", anyone seen anything similar?
Cheers,
Teric
P.S. Could it be a scaling issue, perhaps?