Had came across with the similar issue with VB
application + oracle + crystal report 8.0. Here is what I found out the root cause of this behaviour of some reports being sent to printer but some not.
1. Open the Crystal Report in the desing mode
2. On the file menu click on "Printer Setup"
3. In the Printer Setup dialog uncheck the "No Printer" option
4. Save the report and exit
I think this should solve the problem of some report being sent to printer while some not. If the "No Printer" option is checked then the report will not be sent to the printer.