"Email" field not showing under Membership > Payment Gateway > PayPal Payments Stand

Hi,

I am trying to configure "PayPal Payments Standard Gateway" but "Email" field is not visible only (Under Membership > Payment Gateway > PayPal Payments Standard Gateway).

Please check below screenshot >

http://4.bp.blogspot.com/-SY9Fel2KpME/VFsYh5G1R_I/AAAAAAAABBk/UxJmt-jIBYk/s1600/paypal%2Bmembership%2Berror.jpg

Please help.

Regards,
Neha K.