I've never had this problem before, in fact earlier today it was working just fine.
When I go to upload a video, it brings me to the page where I select what I want to upload it to, so I choose youtube and it tells me to sign in, which is weird because my youtube account and psn account have been linked for almost a year now. So I sign in, and then it brings me back to the selection page, so I click youtube again and it just brings me back to the sign in page again, over and over and over.
I signed in via the playstation network settings and the same problem happened. I also did as many others suggested and removed the access to psn on my browser, and signed in again. Still isn't working.
Now it refuses to even sign me in, it skips the part where it brings me back to the selection page, and just goes straight back to the 'sign in' page as soon as I sign in.