Subtitle Darking the image URGENT

Hey,

I'm about to deliver some dvds.
But when there is subtitle the image is darkens.
Like it lost light or something.
The second subtitle appears it darkens more in the same cut.
How come this can happen?
Please let me know it is very urgent.

More info is needed.
1. Do you notice this darkening in the actual timeline when you play the project back or are you only seeing it on the encoded DVD?
2. What are the details of your project ? Size?, etc.
3. What version of OS and FCPX are you using?
4. What title(s) are you using and how did you apply them? What compositing options did you choose (screen, overlay, etc.).

Without knowing any of the above, it sounds to me like you may have a composite function applied to the title that causes darkening on the underlying video frame (such as a darken, screen or one of the many preset options that can be selected).