PDF PO not generated when triggers from Tools > Coimmunicate from PO Summary

 We manually convert requisitions into Blanket Releases by running Create Release request.  According to Oracle converting request to release this way will not e-mail supplier the PO (in PDF) automatically.  As a work around, we do the following:

1. Go to the purchase order summary form
2. Query the purchase order
3. Go to tools -> communicate
4. Click e-mail, predefined email address populate

5. Clicked OK to submit.

Supplier received the e-mail with attachment, but when supplier clicked to open it, got message "System failed to generate the PDF document. Please contact your system administrator. "

The e-mail function works fine when approving it from PO approval form or release it automatically from planning workbench.