Synopsys Design compiler error "No scan equivalent exists for cell"

[user_2015]

I use nangate library and I see in .lib file that the flip-flops have scan equivalent cells but I get "No scan equivalent exists for cell" when I use Synopsys Design-Comipler. How I can resolve this problem? Should I apply any any changes to .lib file before generating .db file so Design-compiler understands that which cell is scan equivalent of which cell?

Every thing is good if I use anther .db file (called lib2.db) (Unfortunately I do not have the lib2.lib file so I cannot see how the scan cells have been identified there and change the other library if needed.

I appreciate any help.