It means that maybe something with optification went wrong. This is how things look on my n900:

# cat /usr/bin/7z
#! /bin/sh
exec /usr/lib/p7zip/7z "$@"

#ls -ld /usr/lib/p7zip/7z
lrwxrwxrwx 1 root root 27 Oct 1 2011 /usr/lib/p7zip/7z -> /opt/maemo/usr/lib/p7zip/7z

# ls -ld /opt/maemo/usr/lib/p7zip/7z
-rwxr-xr-x 1 root root 359808 Jan 11 2010 /opt/maemo/usr/lib/p7zip/7z

Please someone having troubles with 7z to repeat the above commands (cat, ls, ls) and to compare with mine. Also did you make some changes to filesystem (ie repartitioning, re-mounting, ...)?

Also I thing a bug should be raised against p7zip-full package so if there is still an active maintainer to help on that one.