If you've pressed down and scraped the transfer tape into the vinyl really well and it still won't stick to the transfer tape just flip the vinyl over and scrape against the vinyl backing too. This often does the trick! If it doesn't, it's often because eitehr your transfer tape has lost it's stick (if you're reusing trasnfer tape), or maybe you need a different brand. It could also be because you transfered oil to your vinyl from your fingers when you were weeding. Rubbing alcohol across the vinyl could help.