Cisco vlan entry missing in vlan.dat, but appears in running-config

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http://serverfault.com – One of our vlan's (ID: 104) stopped working suddenly and computers on that vlan failed when trying to obtain a dhcp ip address. On the Cisco switch if we do show vlan, this command is supposed to shows the vlans in the vlan.dat file. We notice it has every other vlan except the one that is now missing. If we show the running-config or even the startup config, they DO show the missing vlan (as if everything is fine), but that vlan doesn't take effect. We tried deleting the "missing" vlan using clear vlan 104, but it says No subinterface configured for vLAN Identifier 104, so it's already mis (HowTos)