Your subject heading did NOT say it all.
From reading it, I was assuming that you had put University aside with Prince, but it did not work properly in subsequent turns.
What you meant, of course, was the second possible meaning: that you were not even able to play the University with the Prince. Prince IS working properly here. It can be paired only with a card up to 4 value (which by the way; means you could use a 5-value card if something you had in play had lowered the card down to 4 or lower by the time you played Prince.). All cards with Potion are, by rule, NOT lower in cost than any non-Potion card. I know this seems weird...you mean a 2 + potion card does not cost less than an 11-coin Colony?!? You have to think of Potion cards as operating on a separate track. Completely distinct in "cost" from non-potion cards.
On the other hand (what I think is counter-intuitive), if you Remodel a card that includes a Potion, you can gain any card that is up to 2 coins more in value. So, Remodeling an Alchemist (3 + potion) CAN get you anything up to a normal 5-value card, or any Potion card that costs up to Potion + 5. Confused? Me too, a bit.