Unable to open attachment from Outlook

[uvz]

Hi all

Pocket Outlook don't open more directly nobody attachment.
When I tap on the attachment, a popup say "Impossible to show the attach".
I must save it and launch from file browser to open.
(I set the option to store the attach on sd card).
Maybe I delete somethink in the windows folder (???) to cleanup the old messages stored in ram...
Does anyone know the name of the file(s) to restore from an old backup (or from a clean backup after hard reset) to fix this annoying issue?
...or another way to resolve it?

TIA

(Treo750v- wm5)