The primary cause of mis-aligned labels when you print is your printer margin settings. Most printers cannot print near the very edge of the page. Many applications (including PDF readers) try to compensate for this by shrinking the page when you print. However, LabelMakr PDFs are designed to match the labels exactly, so you need to disable this "feature". This page has instructions for various PDF readers that I have come across.

Use one of the margin test pages to make sure it is working correctly. The printed page should either have triangles going to the edge of the paper, or cut off. If you see all the triangles and the last one is not at the edge of the paper, then you have to change your settings.

Adobe Reader 9.1

In the print options dialog, in the Page Handling section, for Page Scaling, choose "None"

Adobe Reader 9.1 Screenshot