paypal - How to connect to the remote server for express checkout -

everything working absolutely fine in development here on local machine. when migrate code production server @ our hosting site , remain in sandbox mode error.

exception in httpconnection execute: invalid http response unable connect remote server 

i've debugged traces spot in code:

    dim setecresponse setexpresscheckoutresponsetype = service.setexpresscheckout(wrapper) 

our web.config has following entries:

  <add key="paypal_redirect_url" value="https://www.sandbox.paypal.com/webscr&amp;cmd="/>   <add key="e_hosting_endpoint" value="http://localhost"/>   <add key="paypal_api_mode" value="sandbox" />   <add key="paypal_api_username" value="babrams-facilitator_api1.commuter.net" />   <add key="paypal_api_password" value="1395365656" />   <add key="paypal_api_signature" value="a78scs0nuckkjvsrxfqeygq8fap4acirrk.ij6zw7-hjiwaeo0k28aib" /> 

we tried changing e_hosting_endpoint our website domain, same error. tried testing these urls html page on production server , work fine, don't think firewall issue or network connectivity @ fault.

https://www.sandbox.paypal.com/webscr&cmd=_express-checkout&token=ec-4wb48589uh622552b https://api-3t.sandbox.paypal.com/2.0/

the project works fine in development. in production not work.

any insight should for, or how resolve issue appreciated.

have checked ensure curl enabled on production server?