If the ink is too heavy and the lines on the barcode run together as shown here, the space between the bars is filled in and makes the tag unscannable.
Cut off printing
This is the tag on the right edge of the page where the printer stopped short of printing the entire barcode. Make sure the barcode is centered under the words Discount: Yes (or No).
Out of toner
If you are running out of toner on a laser printer or copier, the bars start to lose their integrity. Make sure the lines are crisp and full.
The texture on the paper used for this tag prevented the ink from creating a readable barcode. The color is light enough to be OK, but the texture is causing scanner problems.
This one is less common, and a little hard to see. There are some parts of the print head on this inkjet printer that are stuck and no longer print. Because they make it look like more bars are present, the scanner picks up the wrong number.
The barcode scan is the only way we can sell items (or hand entering the barcode). If we try to change the Discount from no to yes, it will not allow us to sell that item because it is not in our inventory. Also, we have to prevent shoppers from changing discount status with their own pens.
Correct page orientation
Make sure the black lines are visible on both sides of every tag, and that the tags fill up the entire sheet of letter sized paper.
Incorrect page orientation
If your tags print sideways, or leave extra white space on the sheet as shown above, it is likely they will not scan because the barcodes are too small. Also in this example, the black line on the right edge is cut off, which means that part of the barcode might be missing.