I don't usually participate in forums but I respect the effort of people that developing this powerful free application. I had the same problem (entered free account info in premium section. then i got an error "account is invalid". and when I try to download, I got plugin error- plugin out of date). I discovered that this is due to my account was inactive, I could download could from the site though, because I didn't login for 180 days. If this is the case with you, login in with your free account from browser, click on your username and then reactive the account. or you simply can create new account. then you have to add the premium account in Jdownloader again.