Welcome to the Doom9 forums, Marty.
I don't know the cause of this error. Are you sure that you have the latest version of java? (32-bit is OK.)
Try to use the C++ version of BDSup2Sub, and see if it helps. (Change the version to use with the Settings menu. I don't recommend yo use the ++ version, but in this case, maybe there will be a better error message, or it will work just fine.)
What is the source of the subtitle you are converting? I see it's an XML file. I guess you have converted another stream to XML first. What program did you use to do that conversion, and what was the format of the original stream?
I suppose that the error can be caused by something odd in the source XML file, like a malformed string. Have you manually modified it before converting it?
Can you send me the "Titanic 3D.xml" file as well as the 3D-plane file, and, if you still have it, the "temp.3D_left.xml"? (You'll find my email address at the
bottom of the PgcEdit home page.)