I/O warning : failed to load external entity "/root/.radiant/1.4.0/global.pref"
/usr/local/games/GtkRadiant-1.4/radiant: line 9: 8105 Illegal instruction "$radiant" $*
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It is trying to read its preference file in root's home directory when it should be searching your user's home directory. Are you trying to run it as root or as a user?