PayPal Standard redirect gives "The given key was not present in the dictionary" exception

When PayPal Standard redirects back to my site after payment, the following exception is thrown:

[KeyNotFoundException: The given key was not present in the dictionary.]
   System.ThrowHelper.ThrowKeyNotFoundException() +28
   System.Collections.Generic.Dictionary`2.get_Item(TKey key) +7452508
   NopSolutions.NopCommerce.Web.PaypalPDTHandlerPage.Page_Load(Object sender, EventArgs e) in PaypalPDTHandler.aspx.cs:100
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +99
   NopSolutions.NopCommerce.Web.BaseNopPage.OnLoad(EventArgs e) in BaseNopPage.cs:109
   System.Web.UI.Control.LoadRecursive() +50
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

I've seen this exception discussed on a number of posts but I've double checked all my settings and everything seems fine:

In nopCommerce Paypal Standard settings

1) Use sandbox is false
2) business email correct
3) PTI Identity Token same as shown by Paypal

In PayPal settings

1) IPN message delivery enabled
2) IPN notification URL set
3) Auto return enabled
4) Return URL set
5) Payment data transfer enabled

Any help would be much appreciated.


Regards, Chris.

Solved. It's a new PayPal account which I did not activate, i.e. didn't click the link in the email received from PayPal.

So totally my fault, but not entirely obvious as you can use the PayPal account otherwise!

Working perfectly now.