Dell may have a link to the software guide or what about the Help function in the application?
Try this link: http://support.sonic.com/
If you are using a DVD RW, you must format the disk first and make sure that you are not finalizing the disk somehow. Also, make sure you have room on the disk. Another option maybe to write the entire file(s) each time. You may need to tell you unit to overwrite or erase the existing file.