Having a switch from Cisco: SG300-52, It functions only from a web gui, no cli available which has made configurations cumbersome.
We don't see a tab for assigning an IP Address to a VLAN under "VLAN Management".
This document will attempt to track known reasons and workaround/fixes for this error.
Our intended goal via the web gui is: Switch(config)#interface Vlan2 Switch(config-if)#ip address 10.x.x.x 255.255.255.0
Switch runs in Layer 2 mode by default. If we want to put ip addresses on the vlans, need to change the switch mode from Layer 2 mode to Layer 3 mode. We can ONLY do this in the console menu (not the web GUI). It does indeed exist, you must access it using a baud rate of 115,200 (not the standard 9600), data bits = 8, parity = none, stop bits = 1, flow control = None. It is also available via telnet (default username/password is cisco/cisco). Go to Switch Main Menu --> System Mode.
NOTE: Switching between Layer 2 & Layer 3 modes will clear all other configurations that you have in place, so plan accordingly.
You should be able to address the vlans after you've made this change.