There could be a few causes to this issue. For example, the email you're using might not support PDF files or the PDF you're trying to send exceeds the maximum allocated file size attachment per email you send. However, the simplest way to test this is to generate the report and save it to your PC, then manually create a new email and attach the file. You will get a message with an error in case something goes bad. Additionally, the software might be broken and it could possibly send the PDF file in a wrong way.