I’m not working in CS5.5 But the process should still be the same.
If you created your subtitles within Encore, the only way I know to see the full list of settings is this:
Select a subtitle track on your timeline and from the top menu, click Timeline > Export Subtitles. Save the file. Now with that same track selected on your timeline, Re-import the file.
(Timeline > Import Subtitles )
Upon import of this file you should see the FULL range of Subtitle setting options in the menu. The margins will be the numbers defaulted at (72 648)/(48 432) The 72/648 numbers are the left and right margins that seem to cause the error.
Setting them to 92 (left) and 628 (right) has worked for me.
Let me know if this works!