Not generating pdf invoices

WHILE GENERATING INVOICE IF I SELECT DOWNLOAD PDF IT OPENS A LINK BUT NO PROCESS IS DONE ONLY A BLANK SCREEN SAME ISSUE IN EMAIL IF I SELECT EMAIL IN INCOICE MODULE IT SHOWS THE EMAIL FORM BUT AFTER SELECTING NECCESARY FILEDS IF I CLICK ON SEND
ONLY A BLANK SCREEN

https://kpssystems.co.in/index.php/mailer/send_invoice/2
the above is he link i can see on the screen nothing happening after this a blank screen only

can any one help to sort out the issue
i tried some topics like pdfs not generating in that they advised to replace the mpdf.php file that too i tried no use