I get that on my works PC. First click on log out and close the page. Then... If in internet explorer, at the top of the page go to tools > internet options and click delete. Make sure you delete cookies and files. Then go back to PCadvisor and click on log out again and it should work. Make sure you know your internet website passwords if you have them set up for internet explorer to remember them and auto log them. Doing this will mean you having to type them in manually.
SirMetal explained in the original question that he was logged in to an incorrect account on his laptop (because of helping out a friend) and is therefore unable to log in to his own PCA account. Hence why he needs to log out of that account first.