Why are my floor tiles cracked and how can I lay them again so they won't crack
If the tiles are cracking, it's probably (edit: might not be) not just the plywood.  The floor is flexing in some manner.  Tiles need a very rock solid underlayment.

So pulling up the tiles and then pulling up the subfloor and then relaying a new subfloor may not actually fix your problem.

The joists may be flexing (and this is probably the issue) which would cause the floor to crack. 

How old is the building?  If the build is quite old, the joists may be further apart or sized smaller than current code.  

There are a few solutions, once you determine the problem:


sistering the joists
adding cross joists under the existing joists
adding lolly columns under the floor


I fixed a floor on the third floor of a 100 year old house by pulling up the plywood and gluing and screwing half inch subfloor.  The floor was rock solid, but we still didn't put back ceramic tile - we went for black and white vinyl. Looked great.