I have read several reviews from people that are having issues getting the black cartridge to fit. I think I know what the issue is. There are TWO spaces for black cartridges. The one on the very left side is for the PHOTO black, the one on the right side is for the regular black. You can tell because each cartridge has a shape (circle, square, etc) on it which matches the same shape on the cartridge slot. The XL cartridge ONLY fits on the space on the far right.
I LOVE this printer. I was able to print over 300 pages with just the sample black toner that came with the printer. My color cartridges are still nearly full and I have printed some pages that used alot of color. I LOVE the front/back printing option, I print alot of pages for my college classes and this feature saves tons of paper which in turn makes my binders (and backpack) light-weight. The scanner works wonderfully too.