What does the error code E21 mean on Canon Pixma printer?

ERROR CODE CANNON MP150/MP160

E2 - No paper (ASF)

E3 - Paper jam

E4 - No ink

E5 - The ink cartridges are not installed or a non-supported ink cartridge is installed , or the ink cartridges are not installed properly

E8 - Waste ink absorber full, or platen waste ink absorber full «ОК»)

E9 - The connected digital camera / video camera does not support Camera Direct Printing

E14 - The Ink cartridges whose destination are wrong

E15 - Ink cartridge is not installed

E16 - Ink remaining is unknown

E19 - Failed to scan head alignment sheet

E22 - Carriage error

E23 - Paper feed error

E24 - Purge unit error

E25 - ASF(cam) sensor error

E26 - Internal temperature rise error

E27 - Waste ink absorber full or platen waste ink absorber full

E28 - Ink cartridge temperature rise error -

E29 - EEPROM error

E33 - Paper feed position error

E35 - USB Host VBUD over current error - USB

E37 - Abnormal motor driver error

E40 - Other hardware error

E42 - Scanner error