Here's the Prestige Classes and which expansion pack they come with, so you don't make this mistake again:
Shadows of Undrentide
- Arcane Archer
- Assassin
- Blackguard
- Harper Scout
- Shadowdancer
Hordes of the Underdark
- Champion of Torm
- Dwarven Defender
- Pale Master
- Red Dragon Disciple
- Shifter
- Weapon Master