now I have changed back *only* my username and password in the config file - and again the same errors as before:
STATUS 301 "Protocol "" is unknown"
so it must be my username or my password?

=== later:

Now this becomes really odd,
because in some more experiments, I found out that my usual login-password is the problem. It contains an ASCII char which is neither alpha nor numeric nor control char. But: Changing the password to some plain alphanumeric string - all problems gone!

This is IMHO really strange, as with my original password I get that nasty 301 error only for the transfer of plain files, but not for transfering directory structure nor for initial login to the server!
The server login and the transfer/sync of the dir structure went okay. Only the files themselves produced that 301 error.
How can this be?

=> one vague idea: could it be that between
- simple_oc
and
- owncloudcmd
the password arg is not properly quoted?
But even if this were the case, it still remains the question why this only strikes for plain files, not for dir structure... mysterious.