AFAIK, the standard Last.fm plugins are not working (protocol or URL change, I believe).
fdemmer has updated the plugin and it has been working well for me - you can find it here: https://github.com/fdemmer/Picard-Last.fm.ng-Plugin
I have been using the nightly build without any issues for the last few months. It fixed a few issues that were a problem for me, so it was worth it.
Enjoy!
Jami