Trying to add a user in ESXi 4.0 using the vSphere Client, always gave me this error:

A general system error occurred: passwd: Authentication token manipulation error passwd:

The solution is extremely simple. The problem is the error message. It seems to tell us there’s a problem with authentication, but actually, all that is happening is the password is too short or too simple. Making it at least 8 characters is length did the trick for me.