So currently there is no way to login to the forums using your PS4 account.
And when I say currently, I mean it has been for several months by now. I think almost a year even.
I actually stopped counting the months a long time ago

I have tested this with different browsers and some friends to be sure that neither the browser nor the account was the problem.
(Then again the error shows pretty much that it is a development problem anyways, throwing a Parser error)

I have seen some people reporting this bug online, but not in the forum (obviously, as those people can't login)
So is this situation really unknown so far? Somehow that is hard for me to believe.

Regardless of the reason, please fix this problem.