If you're making the subtitles in MacCaption, try the Time Code > Set Blank Frames feature, set it to 6. This ensures at least 6 empty frames between any two subtitles. Not sure why Encore needs it but it seems to help get past this error.
However I still had an issue where straight play of the Blu-ray would work with subtitles, but any Next/Prev chapter or FFwd/Rew during playback would cause the subtitles to stop working until the disc was stopped and started again from the beginning.
Jason Livingston
CPC Closed Captioning
