RE: 9mm Reloading ??
If the slide won't close I'd say that you've got one or more of the following problems: Overbelled/undercrimped and isn't allowing the case mouth to headspace properly, the bullet is not seated deeply enough and is contacting the lands, the cases are too long and need to be trimmed (9mm Parrabellum headspaced of the mouth of the case), or the cases were not resized properly.
If it's occuring with all the loaded rounds, it's probably not case length. I'd start by doublechecking (you did measure them when you loaded them, right?) the cartridge overall length (COL) with a caliper and make sure it's at the published COL for that bullet. I would also use the caliper to measure the diameter of the loaded case at the mouth and at the midpoint of the case and make sure it's within specs as well.
Mike