OMR sheet printing is very precise and accurate job. Printer must understand technical aspect related to OMR. The bubble and timing track must be aligned in all OMR, some time in printing the paper expansion happens and all alignment of bubbles are out. The other thing is the paper cutting, if the cutting error is more than 2 mm then you might be at trouble as the sheets will not be read by OMR scanner.
For more getting instant quote on OMR sheet printing.