How can I fix my Toyota ks777/kr506 knitting machine/ ribber?

I have not used my knitting machine for several years but know it was in good working order when if was packed away.
Setting it up yesterday took a bit of time and requird using the handbook to refresh my memory. However when I offer the ribber carriage up to the main carriage and tighten the screws, the two carriages do not lock together and will not move together across the needles. They come apart as soon as I try to use themWhat am I doing wrong?