Do you have a macro for your tool change or do you have to enter it in manually?
Does the spindle need to be raised to a 2nd reference point or anything?
G90 G30 Z0
How about spindle orientation?
M19
Your tool parameters should be in the 400's, something like #460 - #475 if you have 16 tools... or more if you have more tool holders.
Check your #480, it should be the tool # in the spindle.
Also, check the #481, it should be the tool # that is ready in position for a tool change.
I swear that I wasn't bidding on that nasty old CNC... I was only swatting flies.