A bit of background. A BLF button on a phone has an LED, and the LED changes depending on the status of the programmed device. The mechanism by which this is done in Asterisk is called a hint. So the phone does a SIP SUBSCRIBE to a particular hint which tells Asterisk that it wants to track the status. Asterisk in turn will send a SIP NOTIFY whenever the device status changes, and the phone interprets the NOTIFY to make the appropriate LED changes on the button.
The error message notification is telling you that the phone is attempting to SUBCRIBE to a hint that doesn’t exist, which indicates a misconfiguration of the phone. You appear to have programmed your external speed dial numbers into BLF buttons instead of speeddial buttons.