In case that your LDAP settings fail and VIMP can not connect to the directory service after you switched authentication to "LDAP", you can not log in with your VIMP user any more to correct the settings.
In order to reactivate the "Framework" authentication, you have to edit the according value in the database directly.
Therefore change the value of field "user_authprovider" in table "config" as follows:
s:9:"framework";