[Janusz]

Have you checked the sliders with the seats not installed to see if they move far enough back to get to the back bolt hole? I would have agreed with Ernie and Art having run into this myself. If you put in the front bolts first, the slider hits the front bolts, not allowing the slider to move forward all the way to get to the back bolts. The front bolt holes slide out further past the seat, so installing the back bolts first still gives you enough room to access the front of the slider. Must not be the case in your situation, so good luck.