PCBCheck 3.21 can be installed directly over PCBCheck 3.x.  
All users should run SETUP.

PCBCheck 3.21 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 3.20 over PCBCheck 2.xx or earlier, you will have
to reconfigure it as all previous configuration information will be lost.

***** SPECIAL WARNING FOR PCBCHECK 3.00 AND 3.01 USERS ******
PCBCheck 3.21 corrects some errors in the default parameters for ARJ and LZH
To make those parameters take effect, you must either delete the
PCBCHECK.INI and run SETUP to rebuild it or reconfigure ARJ and LZH from SETUP
To reconfigure ARJ and LZH to use the new parameters run SETUP, disable 
(delete) the ARJ and LZH scanning capability, then add new archivers and 
enter ARJ and LZH as the extensions.  SETUP should automatically populate 
the settings with the new appropriate settings for ARJ and LZH
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