probably my fault ;D
with the checkbox "Enable two factor authentication (one time passwords)" ->>> "admin - security" disabled it is still possible to configure two factor authentication in profile and more significant: the login form doesn't show the form field but tries to validate it.... result is: impossible to login :-[
Potentially related error in the log:
Notice: Undefined index: otp_timestamp
http://www.elkarte.net/community/index.php?action=login2
File: /.../sources/controllers/Auth.controller.php
Line: 224
yet another one: the re-validation after logout (cookie lifetime) will not ask for the 2nd factor.
Is it still broken or was it fixed?
Schould be fixed