Hmmm, sounds a bit difficult to tell from here, but maybe more could be learned if you would use tce-load -i vlc.tcz from a shell (which should be equivalent to what you've attempted via the GUI) and post the results back here.
Or, to go even further in the troubleshooting, run: sh -vx /usr/bin/tce-load -i vlc.tcz > log 2>&1 and attach the resulting 'log' file here.