Installed LM14 2 days ago. Everything seemingly went well.
Today when checking the update manager I receive: Incorrect password... try again.
I receive the same error using a sudo command in terminal.
I have no trouble logging onto the system with the exact same password at boot time.
I've rebooted, restarted Cinnamon, and Restored all settings to default with no luck.
TL;DR Password works at login, not for anything else.
Thanks for the help.
The password was initially set using the English (International with dead keys) keyboard driver (the default on install - which is really stupid, by the way). After boot I switched to another English keyboard driver which echoed my password exactly as it was supposed to.
Solution: Switch back to the English (International with dead keys) keyboard driver and retype your password in LibreOffice and see how it appears. Now reset your password (Terminal -> sudo passwd <username>) using as your 'Old' password the one created on the Dead-key keyboard.
This is what worked for me.