It is possible you havent all the libraries you need loaded in the library manager. Often a library part refers to another library item or macro. Hence the error message only when trying to generate the library part and not when the manager is loaded.
You will need to track down the missing items. Try opening the library part (opt/command o on mac) and look at the line in question
Cheers John
John Hyland : ARINA : www.arina.biz
User ver 4 to 12 - Jumped to v22 - so many options and settings!!!
OSX 10.15.6 [Catalina] : Archicad 22 : 15" MacBook Pro 2019 [/size]