PDF Creation using to_pff_pi not working

[eluser]Unknown[/eluser]
Hi,I am using to_pdf_pi for generating pdf.Its not working.In some browsers its leading to blank page and in some it shows an error like this " Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 16 bytes) in /var/www/mysteryShopper/system/plugins/dompdf/include/frame.cls.php on line 174"
Can anyone help me plz