I am trying to upgrade my site from 3.6.5 to 3.7.2, after uploading the upgrade package and inputting the administrator username and password, I get a "403 access forbidden" error. I think this must have something to do with some folders' permission not correctly set. But I've checked the
tmp folder, they are all writable, also I've checked the "folder permission", everything is writable here. So I am really stuck here.
P.S.: Live upgrade is not available to me, for some reason, every time I try live upgrade I get a 500 error. This is beyond the scope of this question.