It's possible that the printer was reset back to default. Read the manual for default password when initially setting up WiFi access. Go in and reset to your desired password.
Else, someone hacked your printer and changed its password (just for giggles maybe). Then go into printer config menu (read manual) and reset to defaults, then setup again, using a more comprehensive password (read: harder to guess/crack).
Answers & Comments
It's possible that the printer was reset back to default. Read the manual for default password when initially setting up WiFi access. Go in and reset to your desired password.
Else, someone hacked your printer and changed its password (just for giggles maybe). Then go into printer config menu (read manual) and reset to defaults, then setup again, using a more comprehensive password (read: harder to guess/crack).