Take a look at the following thread:
http://splunk-base.splunk.com/answers/1100/why-are-include-pdf-version-of-results-and-schedule-for-p...
I have had this issue before by having the TimePicker module in a place Splunk didn't like which caused the dashboard to be unavailable for PDF delivery. Can you edit your question and post the dashboard XML? It would make it easier to point out anything odd that way.
I set autoRun=true, but it still remains grayed out.
What can be the issue?