OK so I am having quite a strange issue here, basically one of the user login passwords for the machine seems to be getting changed or corrupted every few days (1-3 days) after the computer is powered off. This is requiring me as admin user to log in and reset the password to via the Users & Accounts preference pane. When this is done, the user can then log in but it says that their Keychain password is required. Sometimes this works with a previously used login password but sometimes not with any password, requiring the whole keychain to be deleted and rebuilt, which is all quite annoying as you can imagine. I have tried to eliminate as many possible potential user-error causes which might lead to this behaviour, such as changing keyboards, ensuring CAPS lock is on/off etc., but even using a simple password such as "password" we may come back tomorrow and find that it no longer is accepted by the OS? Anyone have any ideas on how to troubleshoot? I guess I might be able to solve in one way by creating a new user account and trying to migrate documents over to it but ideally would like to avoid that. Thanks.