Today I was changing the run as user for my IBM Connections WebSphere Deployment manager back to the dedicated user after installing CR3 and I made a typo but did not catch it until I started my server up. Or at least tried to start it up.
Failed to look up group xxxxx
Past SetupChildContext and execvp block. An error occurred. Return valuue is:  and sysErr is: 
Creation failure, spawn was unsuccessfull. Therefore deallocating process structure at: ……
ADMU0111E: Program exiting with error:
Group: [xxxxxx] does not appear to be valid on this system.
Process could not be created.
ADMU1211I: To obtain a full trace of the failure, use the -trace option.
ADMU0211I: Error details may be seen in the file:
Normally you would change this on the IBM Solutions console, guess what, this message says you cannot start it. same goes for the wsadmin command available to change this.
There is another place to go and that is your server.xml
In your profile path for your deployment manager go to /config/cells/cellname/nodes/nodename/servers/dmgr/server.xml
You will find a section in the bottom <processDefinition>, your runas user will be listed.