your imap server wants to alert you:invalid credentials

your imap server wants to alert you:invalid credentials

I have configured Outlook to Zoho mail. When I try to access my mail through Outlook , I receive this message: your imap server wants to alert you:invalid credentials. 

It was working find till a week back but now I receive this message everytime I Access outlook. How do I sort this out?

Regards
Vipin