A user of the program, José Carlos Galán, has detected and communicated to us a possible cause for the authentication error. It is that in the new user registration form, the password field only allowed 10 characters. It is possible that some users have created their account with a password of more than 10 characters and of course, when wanting to use it the system has not allowed it, since in the database the password had only 10 characters.
When programming the application, it did not occur to us to think that some user might want to use passwords longer than 10 characters, but it has indeed been shown that this is possible, so we have modified both the data entry form and the field of the database. From now on they support passwords of up to 25 characters – we imagine that will be enough – and there should be no more authentication problems.
Thank you very much for the help, José Carlos :-).