What could make crystal reports create empty reports, at random

So this is the scoop. App written in c++/MFC, using crystal reports. There is a certain report that is mailed out periodically. Sometimes that report ends up with no records, even if records exist. If you print that same report to screen/paper, it prints fine. Ie through

m_Report->PrintToPrinter(nCopies,true,0,0);<br>

But

m_Report->Export(exportOpts);

Creates an empty report. If I get a copy of the customer's database I cannot duplicate. If customer tries the next day, it works? Database i MS SQL Server.

Any ideas?