I have multiple Google email accounts and because Google still things that an email address is a unique identifier of an individual I have only activated Google+ on one of them.
Well with the new Chrome hangout app, it runs as a service rather than only in the browser. I like that and thought it was the solution to help me catch hangout notifications better when not working in Chrome. But today, Google hangouts signed into the wrong account, the one that is not Google+ enabled. I tried everything to sign out and sign in to the correct account, but it didn't give me any options. I closed the browser and re-opened it, signed out of google, signed back in as the correct account, but still Google hangouts insisted on using the wrong account. Effectively, it neutralized hangout because the account it signed into was not activated for Google+. It wouldn't enable the account to make or receive calls without first making me sign up for Google plus on that account. I absolutely refuse to do that because it is akin to having three Facebook profiles. Which one of me are people supposed to friend?
After a a while, I finally found the solution. When clicking the green hangout button on the Windows taskbar, if you sign in to Google hangouts ( albeit with the wrong account), right underneath the option to join Google plus there's a button that says learn more. Click that and will open a webpage that is signed into the wrong account. In the upper right-hand corner of the webpage log out of the account, and then log back in with the right account. Now you will have said Google hangouts straight. I'm sure they will fix this bug quickly, but in the meantime I have a workaround.