I assume that you removed the U3 software using the program which I understand is on the actual drive itself, but following that I don't think that I can help you further I am afraid.
Certain drives have proved to be problematic I know, and I suppose it is always possible that you have a faulty one.
This is a process that a lot of users have performed without any problem, but I know that does not help you at all.
I do notice that you have even tried to format the drive to one of the Mac formats, which might be causing a problem, as I am not sure what 'level' TransMac is working at.
Perhaps someone else can help, or suggest something else which you can try?