Even though I'm able to view the sample PDF in mail settings, I see this in the bottom of email when attaching PDFs:
An error occurred while generating a PDF of this report:
Failed to fetch PDF from appserver:
Is it possible that the report is too large to generate a PDF for?
well, yours might be unusally large.
There isn't an explicit restriction around size -- rather there is a default timeout around how long it takes searches to complete. The basic steps to troubleshoot PDF are:
Common problem resolutions: