For everyone interested I modified the teac firmware upgrade to 1.0C so it can DOWNGRADE 1.0D firmware to 1.0C.
If you have a site and want to put that file online, drop me a message and I will send it to you.
By the way,
I compared 524E 1.0C and 540E 1.0C they are almost identical but the size is different: 524E = 512Kb 540E = 1MB
I wonder if there's anybody investigating on this subject.