PayPal auto return does not work for my business account

[timsfcuk]

I have added a paypal button to my website and post the data to paypal using the basic integration offered.  the post data is below.

When a payment is made, customers can return to my website by clicking the return to seller but the process doesn't auto return despite me setting the auto return setting in my seller profile.

The return url is included in the &return value below

Can anyone advise what i am missing to get the process to auto return please

many thanks in advance 

payPalUrl.Append(url);
payPalUrl.AppendFormat("?cmd=_xclick&business={0}", HttpUtility.UrlEncode("XXXXXX"));
payPalUrl.Append("&lc=GB");
payPalUrl.Append("&no_note=1");
payPalUrl.Append("&currency_code=GBP");
payPalUrl.AppendFormat("&item_name={0}", HttpUtility.UrlEncode(basketDescription));
payPalUrl.AppendFormat("&amount={0}", totalAmount);
payPalUrl.AppendFormat("&return={0}", returnSuccessURL);
payPalUrl.AppendFormat("&cancel_return={0}", returnAbortURL);