Having linked your YouTube and Google accounts last year, YouTube has now enforced the use of the latter's password for signing into YouTube from mobile clients such as the Symbian/S60 version (available in, for example, the Ovi Store and on m.google.com). Screens and more info below.
Read on in the full article.
I signed in using my Youtube details then a few days later it prompted for and rejected the same details. I found I could "sign out" in the menu, even though it seemed I was not logged in. Then I again entered my Youtube username and password which were accepted and have been since. Of course, this might just be part of the changeover.
How would one find out there is a new client available?
I'm asking, because I had the previous client on my n97 mini (the one that doesn't support sign in). It didn't have any option to check for updates. Also, when I went to Ovi store and found you tube client (supposedly the new one), it detected that I have one installed and only offered to "Launch"... no info on download or upgrade.
Only after I found out on this site that there is new one available, I removed the old one from the phone and then downloaded new one from Ovi. But if I didn't check here, why wouldn't my phone tell me (or Ovi) that update is available?