Hi there Zaheer.
I had the same problem, I found that I had to change user permissions for a file called Phantomjs
I believe its the pdf "sdk"
I'm using Ubuntu, I'm not sure what OS you're on, but ensure that the file is executable and consider what groups should have access to execute Phantomjs
You will will find the file under <your-reportico-install>/bin/phantomjs
This was in any case my problem as to why pdf was not downloading when doing an export