Hey James,
With tx SE16 please have a look in table TRBAT.
Your original transport was stuck and then you have deleted the .LOB file and tried to reimport. For me it looks like the entry in TRBAT was not rolled back due to the above actions.
If, as I suspect, you will find an entry in TRBAT, please delete the entry and then refresh your TMS queue. It should show as imported then.
After that, I'd try to import again just to ensure that for the next time everything goes through clean without all the manual intervention you have had to go through up until now.
Cheers,
Amerjit