Issue when deleting document revision

Dear all,

i’m new with SuiteCRM and i’m trying to use Documents.
I have seen that Documents uses revisions. What is the right way to delete a revision? When i try to remove

it appears the message undefined


undefined message is related to wrong file permissions, do you have them correctly?

best regards

Same issue…
version 7.7.8 and permission is fine.

Does anybody could suggest a fix?