Thick marks on photo paper

Hi,
You don't say whether the mark is a dent/dinge in the paper or whether it is a dirty or inky mark. If it is one of the rollers pressing and making a dinge in the paper you need to check for flat spots on the rollers. Do check all the rollers as the problem may be caused by another roller not gripping properly or the feed rolls being twisted therefore the one where the dinge occurs is over compensating. You can get rid of small flat spots or shiny bits on the roller by GENTLY roughening the roller feed wheels with a fine emery board. This will also clean off any dirty marks on the roller. You can clean dirty marks off the rollers with a non-lint cloth/specialist wipe. (I use baby wipes). Make sure you get rid of all the dust, as this will cause more marks. Clean the platten glass, again with a glass wipe or windowlene to get rid of any marks there. It is also worth taking out the catridges and wiping the ink surfaces. I use kitchen roll and the a baby wipe. Do test the baby wipe first to make sure that it does not damage the printer. If it is possible without taking the printer to pieces wipe the cartridge feed bars. I use a oil based specialist wipe fro this. Another thing that could cause the symptom that you describe is a piece of debris/stuck paper in the feed path. So check that the path is completely clear. You would be amazed at the impact of even a tiny scrap of paper stuck can have.
If you printer has a clean cartridge utility, do that for both cartidges and run the alignment routine before using the printer again. Print a test page to check that you have got rid of all the marks.
Good Luck Please send me feedback so that I know that this fixed the problem.
Carrie