Hi Tuan-
I just purchased the Payment Form extension, and noticed that the "New" button on the Payments Management screen isn't working. Instead of taking the user to the New screen, it just reverts back to administrator/index.php. I re-downloaded it a couple times and tried installing it both locally and to the web, and was encountering the same issue both times.
I'm not sure if this is related to your component, but after I installed it, my .htaccess file had a "deny all" line appended to it. Is there any way the Payment Form extension could have done that?
Thanks again for your help (as always), and look forward to using another one of your extensions.
Cheers,
Kevin