Missing nozzles are often seen as white horizontal lines in the print. Dark lines can be caused by mis-alignment, mis-firing nozzles or a dirty print head. I suggest you 1. print a nozzle check to see if all positions are fully printing and check for mis-firing nozzles, 2. align your printer to the paper thickness you're printing on and 3. clean the capping station, wiper blade and bottom of the printer head as per our instructions (http://www.inkjetmall.com/tech/content.php?133-Printer-Preventative-Maintenance). After cleaning the printer, print a nozzle check and make sure all positions are fully printing before making a test print to check if the line happens again or is gone.
I have also seen data corruption cause strange artifacts and lines printing that are not in the image file, so if you continue having this problem you should shut down and restart both the computer and printer, flatten the current image file (if it's not already) and also try a different image file to see if it's related to the image.
I hope this helps, best regards~ Dana