Affects : Mac OS X Version 10.6.8

Uninstall the previous QuarkXPress 9 version and then perform a fresh installation.

Please navigate to the following locations and trash the files. Then empty the trash.

• Navigate to Mac HDD >> Applications >> QuarkXPress 9
• Navigate to Mac HDD >> Library >> Preferences >> Quark
• Navigate to Mac HDD >> Users >> Home User >> Library >> Preferences >> Quark >> QuarkXPress 9
• Navigate to Mac HDD >> Library >> Application Support>>Quark>>QuarkXPress 9>>Trash com.quark.quarkxpress.setup.plist file
• Navigate to Mac HDD >> Users >> Home User >>Library >> Application Support>>Quark>>QuarkXPress>>Trash com.quark.quarkxpress.setup.plist file

NOTE: Users>Library folder is a hidden folder on Lion (10.7.x/10.8.x) operating systems which you may need to unhide by navigating to Go menu >> Go to folder >> Type this command ~/Library.

And then perform a fresh installation by downloading the installer for QuarkXPress 9.5.1 using the link mentioned below:
http://www.quark.com/support/downloads/Details.aspx?fid=243