I've been getting this error on my Workcentre 6515 when trying to make double sided copies from the document feeder. The machine is just out of warranty.
As luck would have it, I have another one of these machines. This one with a scanner unit that broke some time ago (again, just out of warranty). At the time I replaced the machine because other than the breakdown I had been very happy with it (ease of use, print quality, paper handling, featues, noise level etc). So: I have spare parts!
The only question is: which part will I need to replace?
