Edited. I fixed it.

 

Can you remove the brake disc from the other side of the car? If so, then you can compare the two assemblies and see what is different between the two.

 

Hummm.... Chances are, the brake shoes are either damaged or the 1/4 turn screw holding them broke the back shield.

You need to post a picture so we can help you further. Without a picture, we are just guessing.
Basically, with the parking brake off, you should be able to install the new rotors.
If they don't fit, you might have to adjust the brake shoes adjuster with a screwdriver (little piece between both brake shoes at the bottom with a tooth wheel on it.)

Good luck

 

Why are you driving with no brake rotors, when you brake you'll blow out the rear caliper then you'll end up with having to spend more money and time...


Like Dragon said you should post a picture, the rear rotors are a tight fit but they should slip in, if not you'd need to unbolt the bracket, if you didn't do that, I have no idea what you did.

 

I am guessing the brake shoes for the parking brake are bent out of position. Post a picture, so we can see what interferes with the rotor.

 

+1, BTDT on my E30 a loooong time ago. Luckily all that I had to do was reshape the backing plate where a retaining pin slipped through it. I have no idea how similar the E60 parking brake mechanism is (probably very) to the on my E30, but I can guarantee that's where the problem lies.

 

Parking brake setup at least on early E60s are the same as any other older BMWs. Nothing special about it, not complex at all.

This should be an easy fix, Worst case is a bent backing plate and missing hardware / broken shoes. Nothing that can be fixed.