Mirroring flanges

Everytime I try mirroring a sheet metal flange I get an error stating
to try mirroring a body. I can't find anything in help that explains
how to do this. Has anyone experienced this before and if so how did
you do it?

 

If you have a sheet metal part that needs to be mirrored you can only mirror
it using an edge surface as your mirror plane.

To mirror the body hit the mirror tool select the edge you want to mirror
over and at the bottom you have your feature selection list by default
expand the body selection list and select your part.

Corey Scheich