When applying icing sheet to cake, it is best to apply on freshly frosted butter cream. If the icing has formed a crust just lightly mist with water or lay a dampen paper towel over cake for a few minutes. Then apply you icing sheet. Be sure to apply from center outward to prevent bubbles.
If you are getting vertical lines on your page, chances are your pin feeds need to be cleaned. The reason this occurs is that the wet ink is causing small bits of icing sheets to build up on your pin feeds leaving track marks going up and down. For detail instructions, go to our website and login under the support page.