Need a lot more information. What version are you using? What tube or pipe style are you trying to populate from? Do you have access to Content Center? What exactly are you seeing when you attempt to populate? What is your general workflow?
Gee... is that enough questions?
AutoCAD 2013, IV 2013 Pro Tube and Pipe - Frame Generator, Vault Pro 2013 Win 7 x64, Dell precision PWS690, GeForce GTX580