Hi I have looked for a resolution and found a post, but I am getting a different error. I am using Joomla 1.5.22 and the latest DT Register version. When I enable Joomla SEF & Re-write and click on the "Register" button from within an event article, instead of going to the registration page I am taken to the calendar.
When I disable the SEF/Re-write it works as it should. I do not have any other SEF components installed.
DT Register works just fine with core Joomla SEF. You must have something else in the mix causing the problem. Feel free to submit a ticket so we can check it out on your site. No one else has ever reported a problem like this.