What can cause a single horizontal bar on color prints?

[Kormak]

Is there any part in a canon inkjet printer that can leave a 1/8 inch horizontal line across on a color print. That is slightly darker to the color that is on the paper. Could it be a dirty bar that temporarily touches the paper?

I suddenly have this single bar on most colorprints about 4 inches from the top. Rest of the print is fine.

 

[PeterBJ]

Could you upload scans of a print showing the error and of a nozzle check?

Could the error be caused by curled photo paper?