I solved my problems, with this re-index instructions. I give a very BIG thankyou to FireDog.
(After reading lots of junk about how to delete those undeletable messages, asking to repair, uninstall and reinstall. I didn't repair the app, the problem was in the data).
I had diverse problems...
Problem A:
Some folders just didn't display any content. Not even "this folder is empty" message. But their properties showed they had XX messages. Of course, trying to empty deleted items was unsuccesfull with message telling "Could not delete... to try later."
Every time WLMail started it showed "Recovering message store...".
Problem B:
Delete a message was impossible. Due to the ·deleted items" folder was damaged.
I noted, "Shift-delete" worked fine, but "delete" won't.
Problem C:
Re-indexing as suggested in your post was not running because "the folder is in use".
So I recalled I readed in some other page to set advanced maintenance option "Empty deleted items folder on exit" to be set. So... I unchecked that option, because this one was preventing re-indexation.
My add to SOLUTION :=) wich worked!!!
Add to step 4. above:
Also make sure the "Empy deleted items folder on exit" option is unchecked.
Happy MessageStore re-indexing.
Javier