Microsoft Outlook not saving password any longer
I found this answer at this site: Optimizing your PC So, I haven't tried it or had to use it, but the process seems plausible.
In some cases Outlook doesn't save your password, even if you enable the option to save the password. This error is caused by a malfunctioning of the Protected Storage Space from Windows. To solve this problem, run the registry editor and navigate to the key HKEY_CURRENT_USER\Software\Microsoft\Protected Storage System Provider. You will find a key with a long name starting with S-1-5-21 which you have to delete (probably it's save to create a back-up of this key by File, Export). In most cases the problem is solved and next time the passwords will be saved. Be carefull: by doing this you will lose all stored passwords. Read the back-up page how to recover these passwords.