IMAC.local is already in use

Question

I keep getting this message every month or so.  I change the Network back to "tg-imac.local" and in about the same amount of time, this error comes up again:
The error reads (it does not use the word ERROR anywhere):
This computer's local hostname "tg-IMAC.local" is already in use on this network. The name has been changed to "tg-IMAC-2.local".
To change the local hostname, open System Preferences and click Sharing, then click "Edit" and type the name in the local Hostname field.
The only option is OK to close the message.
I'm getting real tired of changing it back, and having this message pop up again not too long after.  I do have 2 IOS devices connected via Wi-Fi and have the IMAC connected to my time capsule and then connected into my network box.
Any ideas how to get this to stop happening?
Thanks everyone!

Answer 1

I have the same issue, after reading other posts with the same issue I found a reply that makes sense in my case.  (Pasted below).  In my network I have 2 Airport Extreme routers and 1 Airport Timecapsule (all broadcastiing the same network name to extend wifi and allow better reach around our house for Apple TV's etc), I suspect that my iMac joins one of the 3 devices, and when it rejoins the duplicate name message appears.
Here is the post that tipped me to a possible cause;
Linc Davis 
Re: Keep getting warning message about my Computers Hostname, any solutions please?     May 19, 2013 8:09 AM    (in response to Basil52) 
Sometimes this message means that you have two simultaneous connections to the same local network: probably Ethernet and Wi-Fi. Disconnect the Ethernet cable or turn off Wi-Fi.
Sometimes it happens because a device that gets its network address from the router wakes from sleep, and the address it was using before has been assigned to another device.
Rename the computer in the Sharing preference pane.