Vault won't open

I've been using my pc today and NIS 2014 has been working fine - until now. However, when I try to open my online vault, I type in the password as usual but it just keeps coming back with "Vault Closed" all the time. What's going on all of a sudden? NIS seems to be working ok other than this (e.g. I can do liveupdates).

My pc runs Windows 7 Home premium and my browser is IE11.