If you get the error message as Invalid Username and Password while login from Plug-in, then please check the below things.

i) If you have more no of Active Session, then you need to close those active session by going t o "accounts.zoho.com" ---> Active Session ---> Close all other sessions.  Now please try to log in to CRM from Outlook. Please log out from Zoho CRM ( in plug-in click Zoho CRM--> Logout)  before closing the Outlook.

ii) Still, if you face the same problem, p lease follow below the steps.

 This is one time operation and need not be done again.

1. Close Microsft Outlook.

2. Please download the attached login patch file and unzip the file.

3. Open the extracted folder and double click install.bat file it to your computer 

4. Now Open Outlook and try to Sign in to CRM from Zoho CRM Outlook plug-in . 

Please get back to us if you still face the issue.

Regards

Gokul