Mac OS Canon MP Series WiFi Printer Scanner Does Not Scan But Can Print

Symptom:

I have a Canon MP620 WiFi printer and I can print to it but I cannot scan, even though the Canon IJ Network Scan Utility can locate the printer/scanner, and my computer is on the display of the printer itself.

Cause:

In my specific case, if I am connected to a company VPN (CISCO VPN Client), scanner cannot initiate a communication.

Fix:

Try turning off the VPN connection.