I received payments through Google Checkout but there is not record of it in DT Register Records. It does occur on %80 of the registrations, I had to contact my clients to ask which event they are attending.
You need to update to the latest build. There were issues in that build with all external payment types. Download the latest from My Orders and upgrade. Should be fine from there.
By the way, you really should update Joomla too. 1.5.9? Yikes
I have version 2.7.15b and I experience the same problem. Received the Google payment, but no data. My experience is pretty weird though. From March 27 to April 18 everything was working fine. Between the dates of April 23 and April 27 I did not receive data for 90% of the registration. I updated to version 2.7.15b on Mar 26 and to version 2.7.16 on April 28. How can you explain the problem in my case? And how can I check to make sure it doesn't happen again, because it is a pain in the butt to contact folks for the information that should have been collected.