Scheduling Problem_Authentication required_smtp 530

Hello everyone,

I have scheduled one crystal report before 6 months for Every week(Recurring).

After 5 month of successful scheduling from last one month the status comes 'FAILED'.

ERROR:

address error. [CrystalEnterprise.Smtp]: [Error sending address(es) to SMTP server. Return code: [SMTP 530 - Authentication required.]. Reason: [abcd@xyz.com].]

PS: No parameter has been changed.

And when I scheduled for once, [Not weekly ] It is successfully scheduled.

The same person / Recipient is getting other report regularly.

What can be the problem with that scheduling ?!!?

I am not able to trace the problem, Please Help.

Thank You.