With new user and password OK, when try at session login to use it, get message: "cannot enter home Directory. using /." When press OK button, get: "kstartupconfig4 does not exist or fails. The error code is 3. check.." no more space to right and so just ends like that; when again press the OK button, just goes back to the login screen to repeat everything again.
Have installed everything can find relevant to kde, including the extensive library which, for some reason, wasn't included with initial install, but makes no difference. This REALLY frustrating, and any and all suggestions greatly appreciated.

Did check of additional texts of command line and found that to create a USEABLE new user, you have to include the option -m.
Now it works.

Try going into User and Group Settings and set the home directory and any other potentially problematic blanks there.