More info needed,
What ArubaOS version are u using?
Does your topology is MC<>MC or MM> MC+MC ?
Did u try to add the needed VLANS via CLI?
Did u try to add VLANS via diffrent browser?
Try to go directly to the problematic MC and enter vlan xx after conf t.
or via mm go directly to the MC node and try to add vlan.
(share with us the outputs)