The MLB is the only device that stores the database. The DCM receives the card read, then relays the information to the MLB, which makes the access granted/denied decision, and tells the DCM. Check to make sure the doors are set to Protect, not Lock. Lock disables the door. There are also event/action commands and schedule commands that can disable the readers, set them to card+pin mode (even if the reader doesn't have a PIN pad). Do the doors have door status contacts on them? It might be that they are not showing the correct status of the door, which might prevent it from unlocking the lock (why unlock the door if it thinks it's already open?). The Upload command uploads the database from the MLB to the computer, to restore the database after a crash or onto a new computer if the need arises. I suppose it is possible the DCM is not relaying the access request to the MLB, which would mean the DCM would need to be replaced. Just a couple of ideas to look for.
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