I don't think this is the problem, as I have just run the same command in my environment....
@RECIPIENTS = 'XXX@XXXXXX.com',
@SUBJECT = 'TEST',
@BODY_FORMAT = 'HTML',
@file_attachments = 'C:\WWW.sql'
I used a local login and all worked fine.
Have you had a look at your mail profile and sent a test email?
Business Intelligence Consultant