Hi,
please check if you can login manually on 
vk.com. Sometimes VK requires users to identify or fill in a captcha. For example when you login from an unknown domain or country. VK Player does not reckognize this and assumes he is logged in, but fails to search or playback music.
If you can login via the website, everything should be fine afterwards. Just checked it, it is working here.
If problems remain unsolved, do not hesitate to answer.
Best regards