Just a quick guess, try changing your saveset to MSEXCH:MB/ and see if that works...

What do you see in module log?

There isn't a difference, each saveset should backup all mailboxes

Let I try the saveset: MSEXCH:MB/

And show the result for you

But I do not know the different between two savesets:
msexch:mb & msexch:mb/
?

How can I attach the file to this forum?

What error? Can you show us the module log from applogs (not xbsa messages)?

I try that saveset but the error still returned.

What should I do?

Try using Copy and Paste.

You can't attach it. Instead, open the file, find according to timestamp where the backup has started and copy the relevant data for the session here. If log is rendered, try to unrender it before to make it more readable for people here.