Well this is not a difficult answer at all but i was facing some weird issues with Oracle .Net provider when i had tried to login with the newly created user. Before you try to login with a newly created user in Oracle .NET provider, please first give that user some basic set pf permissions.
I don’t know which is the key permission below, which had successfully helped me in login into the .NET provider interface but here are the permission
GRANT create session TO demo_user;
GRANT create table TO demo_user;
GRANT create view TO demo_user;
GRANT create any trigger TO demo_user;
GRANT create any procedure TO demo_user;
GRANT create sequence TO demo_user;
GRANT create synonym TO demo_user;