pb with sharing buttons plugins

Hi,

I’ve developed my website with Vantage theme. I’ve added the AddThis Sharing Buttons plugin under each post. It uses to work well but now some stange things happen:
– on browser Mozilla the social networks buttons don’t appear underneath my post.
– on browser Google Chrome and IE, I can see them but when I click on Facebook icon to share the latest post, on the FB message excerpt there is the correct post title but the short desciption of the previous post… like a pb of synchronisation.

So I’ve de-installed/deleted the plugin, and now when I try to re-install the plugin it says ‘plugin installation has failed. I tried with another plugin and it seems I can’t add any plugin…

is there a general pb with extensions?

thanks.