TOPIC: IPN Validation Failed

Major problems with PayPal IPN transactions failing (the old -- person completes payment, but no registration appears in DTRegister).

In ipnlog.txt file I see many entries like:

[03/17/2017 2:46 PM] - FAIL: IPN Validation Failed.
...
IPN Response from Paypal Server:
‹���������ÿÿ

Any one know what that's all about?

Also, in my server log files, I see a lot of entries with 500 error like:

[20/Apr/2017:07:40:34 -0400] "POST /components/com_dtregister/success.php?return=2814&Itemid=0&task=notification HTTP/1.1" 500 - "-" "PayPal IPN ( www.paypal.com/ipn )"

Also -- why Itemid=0 ?

When I enable Joomla debugging in System settings, and I call the above URL, I get the message:

Fatal error: Call to a member function getTag() on null in /home/armacan/public_html/libraries/cms/router/site.php on line 315

Digging deeper, I found this post:

www.dthdevelopment.com/index.php?option=...754&Itemid=141#25698

Given that I'm on Joomla 3.6.5 and latest DTRegister, surprising that applying the suggestion in above post seems to resolve the issue with the 500 error....

Now to see if that resolves the missing payments issue.