The Flash plugin you have installed is quite old (April 2012) and there have been numerous security updates since. For Flash Player to work in Opera you'll also need a number of files from the Firefox browser. If you're up to it I recommend you do the installation manually:
01. Close Opera
02. Create these two directories in /usr/lib ...
root@slitaz:/usr/lib# mkdir firefox
root@slitaz:/usr/lib# mkdir flashplayer
03. Download Firefox from here ...
https://www.mozilla.org/en-US/firefox/organizations/all.html
... and extract the archive in your Downloads directory
tux@slitaz:~/Downloads$ tar -xjvf ./firefox-*.tar.bz2
04. Copy these 7 files from the /Downloads/firefox directory to /usr/lib/firefox
libnspr4.so
libnss3.so
libnssutil3.so
libplc4.so
libplds4.so
libsmime3.so
libssl3.so
05. Open a root terminal in /usr/lib and create symlinks to the 7 files
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libnspr4.so libnspr4.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libnss3.so libnss3.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libnssutil3.so libnssutil3.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libplc4.so libplc4.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libplds4.so libplds4.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libsmime3.so libsmime3.so
root@slitaz:/usr/lib# ln -s /usr/lib/firefox/libssl3.so libssl3.so
06. Delete the Firefox stuff in your Downloads directory if you don't want to keep it
07. Download the Flash plugin (Linux 32-bit, GZIP Installer) from here ...
http://www.adobe.com/products/flashplayer/distribution3.html
... and extract the archive in your Downloads directory
tux@slitaz:~/Downloads$ tar -xzvf ./install_flash_player_11_linux.i386.tar.gz
08. Copy libflashplayer.so from your Downloads directory to /usr/lib/flashplayer
09. Open a root terminal in /usr/lib/opera/plugins and create a symlink ...
root@slitaz:/usr/lib/opera/plugins# ln -s /usr/lib/flashplayer/libflashplayer.so libflashplayer.so
10. Delete the Flash stuff in your Downloads directory if you don't want to keep it
That's it. You can check whether your Flash plugin is still up to date here ...
http://www.adobe.com/software/flash/about/
... and keep it updated by simply dumping a new version of libflashplayer.so in /usr/lib/flashplayer.