hello 
nopCommerce does not permit recurring charges against Paypal Standard?
For detail see this thread: https://www.nopcommerce.com/boards/t/3867/paypal-standard-setup-no-payment-methods-available.aspx#29799
I was having issue getting "Paypal Standard" on checkout page Payment tab - turns out it was because the product was marked "Recurring Product"
I drilled down the code turns out there's a if-statement which is causing problem in CheckoutPaymentMethodControl.BindData... the if-statement blocks the proceeds if Cart.IsRecurring = true (which in turn is caused by Recurring product" under product page)
Stack as follows:
>  NopCommerceStore.DLL!NopSolutions.NopCommerce.Web.Modules.CheckoutPaymentMethodControl.BindData() Line 165  C#
   NopCommerceStore.DLL!NopSolutions.NopCommerce.Web.CheckoutPaymentMethodPage.Page_Load(object sender, System.EventArgs e) Line 52 + 0x10 bytes  C#
   [External Code]  
   NopCommerceStore.DLL!NopSolutions.NopCommerce.Web.BaseNopPage.OnLoad(System.EventArgs e) Line 80 + 0xb bytes  C#