Hi Marc,
Did you try to re-import the captions like Kirk suggested, it seems the first time it didn't work?
If you want to reset your preferences, the instructions Kirk mentioned tell you what to do, but as you found out finding the Library directory can be tricky. Here's a, hopefully, simpler way:
To open the Preferences inside your Library folder, a simpler way than described in the post is to open it directly in Finder: use the Finder's “Go to Folder…” command (⇧⌘G) and then specify ~/Library/Preferences as the folder to open. You should then be able to follow the rest of the instructions to the letter.
If you're not afraid of the command-line, I can also give you the commands to type in there to do the same.
Hope this helps,
Hayo