What version of Allegro are you using? Create Detail has always only been able to place items on Manufacturing subclasses unless there is some new functionality available that I am not aware of.
pcb viet nam,
Please read my previous post on this. I would strongly recommend using File > Export > IPF to generate a plot file than load it into File > Import > IPF to loaded it back into Allegro vs. using Create Detail. The very large downside of using Create Detail is it explodes everything into individual draws, including text, which means you will never be able to generate text searchable PDF files.
Hope this helps,
Plexus Engineering Solutions