Rear disc brake rotor rubbing against caliper frame mount? I have bolted the rotor to the rear wheel hub and the caliper mount to the chainstay , however...

when I fit the wheel in the dropouts, there is no space between the rotor and the mount. The wheel won't spin freely.

I can't find a solution yet. Am I using a mount of the wrong width? I haven't attached the caliper yet.
I have a 2010 Gary Fisher that Trek recently warrantied. They provided me with the entire rear triangle of a 2013 Superfly, which by all appearances seems identical to my old triangle. There are differences though. Most notably with the new drop-outs. They are deeper than the original. By just enough that I was also having your exact problem. The fix - recommended by the mechanic at my local bike shop - was a simple, external star lock washer placed in between the axle end cap and the drop-out.