Forgive me if you already checked on my solution below, but It held me up for days, so, I thought I'd speak up.

I had the exact same problem as described in this post. None of my realdrums would generate. The way I solved it was following SolidRock's advice above. But hear me out before you re-check his post.

I didn't do it for awhile because my path settings looked right at first. (and I re-checked many times)

Then I looked really close at the error box that disappears right after it tells you it couldn't find the folder. Gotta look quick. No wonder I missed the drive letter. That's because I was concentrating so hard on memorizing the rest of the message.

I had to attempt to regenerate like ten times before I realized that the error message said it was looking in my F drive.

Literally everything else was using my E drive. But for some reason, not the drum generation.

Regardless, when I actually went to the screen described by solidrock (options/preferences/song generation/paths) all of the paths on the 'select folders' dialogue box were already correctly pointing to my E drive. So how could that be the problem/solution? In spite of that, When I clicked "ok", it must have sent a message to the drum generation code and now everything works correctly.

Hope this is helpful