I will jump in here folks as I have had this occur more than once on one of the two 650 execs I own. Specifically my AN650K7. Had nothing to do with wheel bearing, or incorrectly mounted wheel, or warped disc rotor (although admittedly it might). After undoing the two bolts that hold the park-brake onto the end of the disc rotor assembly, I then deal with the calliper assembly removal. Pretty much from that point on as per the workshop manual.
A couple of things that I have found, one is, make sure that you have reinserted the spring metal shims back into the calliper housing the correct way round. Specifically the one that goes beneath the "top" of the two pads which has to be orientated the right way round otherwise the face of the spring type shim interferes with the movement of the pads along the pins (this might not happen if the two very small tabs on one part of the shim are in place, which is not the case on the shim I have - which might mean it normally can only fit one way -this is not to be confused with inserting the shim upside down). The pins being the pair of retaining pins that fit through the two eyes at the top on each brake pad. Another point is, I loosen the LHS brake fluid reservoir/master cylinder so as pressure is released to more easily readjust the calliper pistons. Taking care though to place something around the base of the master cylinder brake reservoir to protect the plastics and tupperware from any brake fluid spills - don't ask me how I know this. Add to that, best to orientate the bars to a position where the master cylinder brake reservoir is level - helps too.
You're going to have to compress the pistons bake into the calliper to get the pistons as flush as possible with the inner face of the calliper. I do this by using a 'G-clamp' as this seems to work best. As for the other piston for the park brake, this needs to be turned back in using something like a wide bladed flat head screwdriver or a cold chisel or similar. I find this pistion to be particularly resistant to winding back in, but it helps to have a relevant tool long enough with a big enough of a handle to get the purchase that I need to get the piston turning.
The last time this occurred only several weeks ago, where the pads were real tight against the face of the disc rotor and took forever to get on, I found the wheel resistance was too tight. It seems the issue was that I had not compressed/turned the park brake piston back enough, as that was the only adjustment I made after removing the callipers back off again, which in itself was not easy, as those pads were tight. No damage to the disc rotor, but a little light scuff marks on the pads. No biggie.
So in summary, check the pistons are back as far as possible into the callipers, and that the shims are orientated the right way round.