KB ID 0000140
Disabled user <name> does not have a master account SID.
A Disabled Account does not have rights to its own mailbox.
Locate the disabled user in AD users and computers > Right click > Properties > Exchange Advanced > Mailbox Rights > Locate the SELF object > “Associated External account” > Allow.
UPDATE: If you have lots of these you can repair them with the NOMAS tool.
Multiple errors Use NoMAS
This is more of an annoyance than a problem – but if there are a lot of these errors it can kill the server.
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