<font face="Arial, Verdana">So it looks like at least launchd is working, but some other part is different then on Yosemite that causes it not to run.</font>
Installer uses
<font face="Arial, Verdana">/usr/bin/dscl</font>
<font face="Arial, Verdana">to create the user repetierserver which is used to run the server. Doc is from 2003 so I assume you have it as well?</font>
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<font face="Arial, Verdana">In </font>/Library/Application Support/Repetier-Server/logs you should find a server.log file that might give a hint.
To see if server is running execute
ps aux | grep tier
RepetierServer 29 0,0 0,0 2479384 4096 ?? Ss So07pm 0:06.76 /usr/local/Repetier-Server/bin/RepetierServer --config=/usr/local/Repetier-Server/etc/RepetierServer.xml
hope that one of the hints show what is different on 10.6.8