unable to export graphs onto pdf.

I have a dashboard with graphs and tables. when i am clicking on the pdf button  the graphs are missing in the pdf. For this same problem on a different server i have increased the  the time to live of each chart option in cold fusion administrator settings and that worked for me over there. Now i am working on a different server but have same cold fusion administrator settings but still my graphs are missing in the pdf. Is this happening due to any SSL Certificate issue or some Fire wall settings.Can anyone please help me on this?