I have a part, rectangular tube. It`s supposed to be a part of a frame, but when trying to mate it into the assembly I can do one mate. Next mate will pop up with a warning that I have to break another. Don`t know why, because I can move the part freely around, nothing is binding it except the first mate.

Can it have somethinh to say that the part is a tube that has two flex commands in it? It has two bends? FYI, I have not tried to use the parts planes to mate, only surfaces. I can attach a pack and go if that helps.