A number of users have reported problems with wrapping JPEG 2000 files.
This turns out to be a bug in the way the "remaining bytes" counter is updated when parsing the file header. The upshot is that depending on the exact format of the header the file may or may not parse correctly!
This has been fixed and the new code checked in, but due to the current CVS outage at SourceForge.net it is not immediately accessible.
Instead you can download the latest sources from a special page here:
http://sourceforge.net/project/showfiles.php?group_id=65032&package_id=188214