1. Check each report/childreport and make sure that the Report.DataPipeline property is assigned OR AutoStop is set to True.
2. Try setting all Detailband.PrintHeight to phDynamic. It may be that you have a fixed height detail band that is too large to print on a page.
3. As a test, try commenting out all event-handler code associated with the report. Make sure that you are not manipulating the dataset in any manner, while the report is generating. This can cause the report engine to get lost.
4. Save the report under a new name and try incrementally simplifying it until the issue goes away. Then incrementally add complexity until you isolate the cause of the error.
If you still have an issue after performing the above steps, please create a simple, minimal Delphi project and e-mail to email@example.com in zip format.