Well, i just experienced a similar behavior in our environment yesterday.
Due to a DNS problem and a restart of the NW services on the server, NW 
assigned existing CIDs to other existing clients.
It obviously (invisibly) misarranged alias names as well.

During a backup, i saw that it was was running fine. However, when i compared 
the client from the group status window with the one in the save sessions 
window, i found out that the client name here was a different one.

Let me suggest that you verify the backup time and query mminfo for the client 
name.

However, if these are new clients, let me suggest that you just delete their 
index directories. NW will recreate new ones.

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