Final answer:
The command is rejected because it's incomplete; a valid IP address and subnet mask are required to configure an interface. The correct syntax includes both values and must be entered in interface configuration mode after selecting the appropriate interface.
Step-by-step explanation:
The reason the command 'SanJose(config)# ip address' is rejected by the device is that it is incomplete. When configuring an IP address on a network interface, you must specify the actual IP address and the subnet mask. The correct format for the command should include an IP address and a subnet mask, looking something like this: 'ip address 192.168.1.1 255.255.255.0', where '192.168.1.1' is the IP address and '255.255.255.0' is the subnet mask.
Moreover, it's important that the IP address and subnet mask match the network requirements and do not conflict with other devices on the network. Additionally, this command must be entered in the interface configuration mode, which is typically accessed by first entering the command 'interface' followed by the interface type and number, such as 'interface GigabitEthernet0/1' before setting the IP address.