2.0.26a - Same issue here. Payments are received into account, payment confirmation from PayPal is received by the shop, but payment confirmation is not sent by PayPal to the user and PayPal reports IPN error to following URL:
http://www.sitename.com.au/index.php?option=com_virtuemart&view=pluginresponse&task=pluginnotification&tmpl=component&lang=Another thing, when refunding a payment, that notification is received fine by both the shop and by the user.
I have 3 emails on PayPal account, same as last 5 years, regular clients and my own tests all produce this issue, and were not present before VM 2.0.26 (updated last week)
It cannot have anything to do with upper/lower case or with multiple email addresses on PayPal account as it was not an issue before as far as PayPal or users are to blame. It must be something in the plugin itself (and only line found is the one already reported which doesn't match the suggestion). I noticed that code is actually
if (strcasecmp($paypal_data['receiver_email'],$this->merchant_email)!=0 ) {
strcasecmp is case sensitive string comparison, I have no idea, but if anything, that might be the issue?!? I tried replacing with this but no difference
if ($paypal_data['receiver_email']!=$this->merchant_email )