Sorry. Cannot help. I dont use total commander as windows explorer does all I require. In my customised view (Show drive letters) I would not need the choice of name you are using -it shows the drive letter.
I renamed mine no problem using WE. U might stoop to WE and try it, then u would know if it is a TC problem.
Also, it shouldn't matter, but if u are not logged on as admin u might try right clicking and selecting RUN AS ADMINISTRATOR