Circular Pattern Tool

Hello, I am trying to use the circular pattern tool to copy fan blades around the rotor of a fan.
I use the
Insert --> Pattern/Mirror --> Circular Pattern

I then try to define the pattern axis by selecting the centerline but it will not accept it.
I can only select three dimensional objects.

can someone help.

Thanks,

Take a look at this and if you think this could help i'll send you a copy. but i would like to ask, are you trying to do this on a assembly or just a part feature?