PCBCheck 3.23 can be installed directly over PCBCheck 3.x.  
All users should run SETUP.

PCBCheck 3.23 is incompatible with all previous versions of PCBCheck.
Though it can be installed over PCBCheck 1.x or 2.x, it no longer uses
PCC files or the PCBCHECK.CFG file used in those versions.

If you install PCBCheck 3.23 over PCBCheck 2.xx or earlier, you will have
to reconfigure it as all previous configuration information will be lost.