I too have this frustrating problem. This has cost my corporation over 100 hours in support time over the last week and a half trying to resolve the issue. I am very concerned I recommended this extension to the client whose registration I am posting this for as we used 2.6.9 without any kinds of problems like this and they are exacftly what the rest of the users in this forum are describing.
I was overjoyed when I saw it was [SOLVED]. Solved how? I would love to provide details but when I debug using NetBeans 6.9 I never can get a break-point that will stop where the issue is occurring. It just shows the total registration cost is message followed by the amount and then a blank screen. I am an experienced developer with LAMP and Joomla since it began as a CMS, having also written components, modules and plugins for the MVC Framework and this has to be the worst issue I have ever seen in any Joomla extension and I have worked with all of the most popular ones at the core level. The worst part is it It disappears and then mysteriously reappears and once it starts, it is a matter of closing the browser, clearing the cache, rebooting and then it mysteriously stops. This reeks of a problem with sessions. I have turned on php.ini settings to display errors and get nothing. I also have turned on error logs and often get nothing. At other times I get dozens of errors.
I will spend the time to logically debug this issue and resolve it for I am not going back to a previous version after the work I have already put in to this. I also went to the extent to rebuild all the DT Register tables, clean up the site, ensure Joomla was upgraded to the current release and Voila, the problem was gone. It worked perfectly and then, after deleting some of the test registration entries I put in (I tested this on a MAC using four different browsers and did the same on a Windows machine, both with the PayPal Sandbox and Live), and entering some registrations manually using the back-end that had been lost, plus seeing three registrations go through without a hitch, I received a support ticket a few hours ago and the same exact issue is back!
My support rate for this client is $100 flat per month and I am now down to $1 an hour this month with this being the reason. I find it hard to believe this could have been released and this problem went unnoticed. I had it happen to me right after the upgrade and now again after rebuilding all the tables, repairing all the database tables, etc. Totally unacceptable but I will get this resolved. If this was [SOLVED] and I challenge whoever said it was, what is the resolution. If I have to upgrade this one more time I will and pull my hair out while doing so. I also don't see how that will correct anything as a user post on 1/26/2011 said it is also occurring on 2.7.2d so what is the point and why is this marked [SOLVED]. I see no one debugging this, using error logs or anything I haven't already done with no results. I also rebuilt everything?
I realize as a developer this needs to be resolved using logic so I am going in again and using NetBeans to debug and I will break-point this to death until I can pinpoint and resolve this issue. I'll have more to report after I am sure my corporation's profit on the support agreement it has with this client is down to 25 cents per hour. This is not something I would expect from a commercial application that I felt was an excellent product and was reliable with the 2.6.9 release. I wanted to use the PayPal Pro feature which works great when you can get past the confirmation page, as does PayPal Standard I want to now use as a a fallback. So, I am can't go back now as the client loves the PayPal Pro but is very unhappy with the mystery blank page and the amount at the top that seems to come and go like the wind.
Joseph J. Geller
Stony Creek Consulting, Inc.
Business and Residential Computing Specialist