Getting Blank Page while submitting my paypal page

[Exportaid]

I am getting Blank Page while I was submitted product form, it's not redirect to PayPal site. I have faced this problem since last 3 days I am using sandbox testing site for testing payment. It shows me the error in network 500 INTERNAL SERVER ERROR. Please Help Soon. 

[elsharkawey]

i have the same problem i tried all buttons types and in firefox and chrome and still the same problem