There are three things that can compete and cause a conflict in the display characteristics:
[li]the DVD MPEG2 data[/li][li]the DVD player[/li][li]the TV screen.[/li][/ul]Firstly, you should do the easy thing and check the options/settings in the last two of these and see whether letterboxing is still selected anywhere (you need it to be deselected, obviously).
If this doesn’t work then you need to check the DVD itself. In the IFO file there is an extra bit in the bytes that store display information that can force letterboxing.
[li]Use IFOedit again to open the IFO file of VTS_01_0.IFO[/li][li]In the top section of the screen select the line VTS_MAT[/li][li]In the lower part of the screen, double click on the line 00000 200, which holds the display information.[/li][li]You should get a box with various options (see diagram below. Is there a tick in the ‘Automatic letterbox’ box?[/li][/ul]If there is, then you need to copy the VIDEO_TS folder to your hard disk, navigate back the same place, uncheck the box, save, and finally burn back to DVD.