When you try to enter the serial number into the CAS VA, you get the following :

Welcome to the Blue Coat ProxySG.
This is a new Virtual Appliance
Please enter the serial number: xxxxxxxxxx
Invalid serial number.

Please enter the serial number:

It is possible that a wrong VA image is deployed. In the example above, a ProxySG VA is used, hence it rejects the CAS VA serial number.

Ensure that the correct CAS Virtual Appliance is installed.