The user credential provided while adding an Exchange organization in the ‘Organization Settings’ page or the account used to configure Exchange Reporter Plus as a service is hidden from the Global Address List.
Verify if the user whose credentials entered in the 'Organization Settings' page, has a valid mailbox which is not hidden from the Global Address List.
To unhide the user from Global Address List,
Fill this form, and we'll contact you rightaway.
Our technical support team will get in touch with you at the earliest."