Can't sign i

Can't sign i

I have the Outlook 2013 plug-in, all installed and loaded well, I have the add-in ribbon.  When choosing to log in however, it does not recognise my credentials, the credentials are correct, i log in online no problem but i cannot connect to my Zoho CRM through Outlook.  DOes anyone have any advice.  I have re-installed the plug-in to see if that helps but to no avail.  Many thanks.