When the printed text does not line up with the places it should go on your pre-printed tags -- especially if it did in the past but mysteriously no longer lines up --  the most common problem is a Printing Preferences setting in your printer driver.  If there is a setting for 'Scaling', Print to Fit Paper Size', or 'Zoom', make sure it is set to 'Off', 'Original Size', or '100%' -- whichever will make sure there is no resizing happening in the driver.  This setting is usually found under the Advanced tab in your printer's printing preferences.

Accessing Printing Preferences:

Windows XP: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/app_print_changing_settings.mspx?mfr=true

Windows 7: http://windows.microsoft.com/en-us/windows/choosing-print-options#1TC=windows-7

Windows 8 (HP printers): http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&dlc=en&docname=c03438017

If this does not correct your problem, you might have a non-standard tag layout, or your tag supplier might have changed the tag layout slightly.  Be sure to compare new lots of pre-printed tags with your old ones just in case!  If your pre-printed tags are not exactly one of the supported standard layouts in Shellstock Tags, then you will need a custom version of the software.