Hi Don,
I tried the options that you have advised too,but still no luck. 
I tried to impose some delays between pdf generation steps,but still the dll was held by the app and now its saying 'System out of Memory'
Now I am thinking of another option-Merging all the individual reports to different pages in a single file that shows up in the screen as print preview and then it can be saved as PDFusing the Export screen.
Here there is a catch-this print preview with multiple pages need to be exported to multiple PDFs.
When I searched thru the web for this option,I cudnt get any such functionality .
Can you please help me on this option to resolve this issue?