Hey Pierre,
It seems like I also can't able to login in your site, and keep hitting this following error :
The most recent request was denied because it contained an invalid security token. Please refresh the page and try again.
Based on the error message, it actually stored the user session in your database and never logged out before, so I unable to login in your user account in frontend, then I found out the reason it keep stored that user session is because of your cache.
I temporary disable with your cache settings from backend > system > global configuration > system > cache setting to NO, and disabled with your cache plugin (system - page cache).
After cleared the cache, the login is work fine now.
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I found out the reason why you hitting that that second error message after login is because this user "hl7news" do not assign under any Easysocial profile type then throw this error.
In my suggestion, it would be best if you can create a new user through your site frontend or backend so this error will not happen again.
Hope this help.