Casting level and a ranger

[temnix]

I want characters to cast a custom spell (of the priest type) at their normal level, which should be the cleric (or druid) level. Well, it works for druids and probably for clerics, but not for Minsc at level 8, already able to cast priest spells. There is nothing different about this spell, the ranger class must be the reason. The spell's ability is for the 5th level. Who knows what is going on there? When is Minsc going to qualify as a 5th-level priest? For the purposes of casting level.