The first thing you need to do is figure out if this is an application/software problem or a hardware problem. To figure this out I suggest you try printing photos on the same paper from a different application or PC.
If the problem is recreatable from a different machine then you know the problem is on the printer or the photo paper you purchased.
If a different machine can do the same function without problems then it is a software issue on your initial machine. In that case contact Iphoto for support and configuruation suggestions.
It is unlikely that the problem that you mentioned is a roller problem. Roller problems are not consistent as slipping and gripping the paper usually results in jams more than print defects. Id place my bet on the paper not being correctly configured into your application for printing as it most likely needs a different temperature or setting to be applied for best results.