[SOLVED] Error: NOTE: Failed to notify 'operator' via email. when trying to send e-mail when job fails

I have a problem with sending notification when the job fails. I created Database Mail Profile and assigned it to SQL Agent and the restarted SQL Agent. When I run a procedure msdb.dbo.sp_send_dbmail the e-mail is being sent. Also when I send a test e-mail using Database Mail it works fine. But when I set a notification for Job when it fails, in job log I see following information: NOTE: Failed to notify 'SQL Job Failure' via email. I don't know what can be the source of this problem. I found this hint: http://sqlblog.jfperry.com/jpsql/post/2009/04/07/NOTE-Failed-to-notify-7boperator7d-via-email.aspx

But I checked that the profile is enabled in SQL Agent. SQL Agent has been restarted. Where can be the source of the problem?