Focus problem or diopter problem?

I recently bought a 6 with a 50mm, I shot two rolls of velvia through it and almost all the shots were out of focus. I sent it to precision camera works to get it adjusted because I assumed the rangefinder was out. They called me yesterday to tell me that it was already spot on. Just before I shipped it to them I realized it had a -1 diopter in it so I took it out without thinking to much about it because I assumed the rangefinder must be the issue but now I know different. Could that diopter have been the whole problem or is a -1 diopter not enough to cause this. I could see the ghost images in the finder just fine with the diopter in.
Any input would be greatly appreciated.
devorobin