Hi TeamSpeak friends,
Recently setup a TS3-Server and experienced a error, Google and Forum search came up with many results and it seems to be a well known and recurring problem.
The solution on the knowledgebase seems to be useless for ~90% of the users.

So I've decided to share my solution to this in hope it helps and maybe gets added to the knowledgebase.

ERROR |Accounting    |   | License already in use, server will shut down
ERROR |Accounting    |   | local accounting reports an already running instance, instance will shutdown
ERROR |ServerLibPriv |   | Server() error while starting servermanager, error: instance limit reached
Screenshot #1 - Error
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I've read that it is necessary to mount tmpfs in/on /dev/shm. After quickly checked and noticed that it already is there, so this answer was useless for me and as it seems also useless for most other users.

My solution!
Connect to the server you want your TS3-Server to run and go to /dev and type ls -la.
Now look for shm and you should see something like shm -> /run/shm

Screenshot #2 - /dev/shm
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Go to the directory the shm was linked to, in my case it is /run/shm.
Again type ls -la and you should see a file with a name made up of numbers and lowercase letters.

Screenshot #3 - /run/shm
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Delete this file!
rm [filename]

Try running the TS3-Server again.

My machine:
Debian GNU/Linux 7.4 (wheezy)
Linux 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2+deb7u2 x86_64 GNU/Linux
Would be nice if you could add this to the Knowledgebase (seems to be down now) or a FAQ.