The authentication endpoint Username was not found on the configured Secure Token Service (CRM Online)

Hi Experts,

I am getting below error in ONLINE 2015 organisation for Plugins.

"The authentication endpoint Username was not found on the configured Secure Token Service".

I am getting this error message for every operation performed in plugins. I have tried retrieve,create and delete but while debugging or without debugging just getting same error message.

Thanks for your valuable responses.