Necromancer – “Invasion” [Campaign 3, Mission 3]

Just in case: do you have a mod installed that unlocks campaign heroes?

Yes, I have a mod that unlocks campaign heroes for single-player scenarios. And another one that allows playing all campaigns through version 3.0.
People above mentioned that only the core heroes need to be recruited, but I completed all campaigns twice in version 1.60, and I don't remember what dragons were there, but I didn't have any problems:mad:
P.S. Maybe I shouldn't have visited the Sphinx with Isabella, I don't know anymore, but I got her 15K experience points there and sent her back to Mythgard.