I'm trying to make a character with hermetic theurgy using metacreator, when I try to give him an "Invoke the spirit of" spell it tells me I need Invocation magic too. From reading the section (pg 78-79 mysteries) it appears you don't need the invocation virtue, but if you do have it you can add names of power bonuses.
Is this a bug in metacreator or am I reading this wrong?
you are certainly right - you only need Hermetic Thuergy.
If you have Names of Power, you can add name bonuses to Theurgic (Invoke Spirit of Spell, Invoke Spirit of Form, Invoke Daimon) spells;
if you have Invocation Magic you can add Name bonuses to a wide range of spells.
but do please report Metacreator bug on their Beta forum.