Can't we use Generics in Avalon-MM slave interface template?

I had my system working. My system is in VHDL, now I am adding Generic declaration in entity declaration. The file can be synthesised. However, when I compile, I get error complaining the size of my signals are not right. I feel that the generic setting is not working, the signals have the length I set before I added generic declaration.

Has anyone experienced this before?

Thanks:)