In our first game a player researched the Printing Press tech in order to build a University in the next turn. However she hadn't researched the Writing tech before which unlocks Library, this is allowed in the game, so she had not any Library to upgrade at that moment (University is the upgraded version of Library).

There was no University card in market place but Libraries. I didn't allow her to build a University by paying the 7 production point for it and picking up a Library card from market place and placing it on the map with the appropriate face up. I told her she should wait until someone builds and loses a University, but I'm not sure, I was right.

So, is it required to have an upgraded building in the marketplace to build it from the ground?

As far as being available in the market, the Library and University tokens are the same. In the same way, if all 6 Libraries were out, then no one could build a new University (they could only upgrade the existing Libraries).

The player should have been able to build a University.

Ok, thanks. So, I was wrong.

Just to clarify, your friend still wouldn't be able to build a library; instead they would directly buy a university for (11?) production.

Additionally, when you research a tech that gives you a building upgrade, all your existing buildings of that type are upgraded for free immediately. (from your original post it sounded like you might have been using build actions to upgrade the libraries)

No, we wouldn't have been using build actions to upgrade existing buildings, this part of rules were clear. The player had no Library when she researched the tech which unlocked University.

Thanks for your explanations, however.