Reports will not email

I have created a report, added a valid email, performed the test email successfully, but when the scheduled report runs I get the following in email.

Dear User,

This is an automated mail generated by Netflow Analyzer Report Generation Engine.
Problem while sending the report.[ Problem could be of large File size

Report details:Report Type :Consolidated Report
Report Generation Time: Mon Jul 28 06:15:29 CDT 2008
***************************************************************************************

Thanks,
NetFlow Analyzer

I can log into the server and manually send the reports from outlook express with no issues.