DLink Switch Not Showing MAC Address

I received this email upon coming into work this morning:

Josh,

See if you can determine why we don?t see a MAC address in the D-Link 1224-TS Gb switch for some ports that have a NIC plugged into the port. We were looking a MAC addresses under Security>MAC Address Table>Dynamic Forwarding Table.

Thanks!

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I don’t know much about this type of stuff yet. I am only desktop support. Any ideas???

Thanks…