I have exactly the same problem
So far I've determined that there are probably some problems with .XML files for buttons, referring to nonexistent files OR some files has not been installed.
Could someone with working button styles dialog check if he has the following files on disk (when opening Button Styles dialog, MyDVD tries to access them, but they are not on disk):
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_home.png
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_home_selected.png
\Roxio\VideoUI 9\Content\Overlays\Masks\Bouquet-K2_chap_btn_mask.png
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_chapter_frame.png
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_chapter_selected.png
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_forward.PNG
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_forward_higlight.PNG
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_backward.PNG
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_backward_higlight.PNG
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_upward.png
\Roxio\VideoUI 9\Content\Buttons\Bouquet-K2_upward_selected.png
X.
Speaking Of Morons........