in the paragraph "Joining Domain Fails Because of Existing Machine Account" it reads
"Further, if the machine is already a “member of a workgroup” that is the same name as the domain you are joining (bad idea), you will get this message. Change the workgroup name to something else it does not matter what reboot, and try again."
this statement seems to be wrong, as discussed on the mailing list, see "workgroup > join domain with same name = no issue? I don't get it" last post from today (after half a year of silence).
This documentation is obsolete, and the string is not in the tree.