[Mr.Fixit]

The problem is often wheel studs that aren't perfectly aligned / straight. If you get the wheels on there, driving around on them usually straightens them out. The drive pins come in different diameters. The black ones are a little smaller than the silver ones. I recommend agaist grinding the wheels or drive pins to make them fit. If you put antiseize on the drive pins(you should) you can sometimes see which drive pins are not going into the holes, a light tap in the right direction with the lead hammer on the drive pin in question often makes all the difference. They can be hard to put on the first time, but after that they go right on and off.