Let me ask this question.. If I add a new user, with admin like rights to an install of APEX and it comes back with invalid credentials.. Does that imply that something is NOT right here??
I do not know, I have not never test add users to INTERNAL workspace using other tools like SQLplus.
How you did add user?
Link to article... ATK's ideas: How to Add Another Oracle APEX Admin User (APEX 4.X)
Issue resolved late last nite.. Co-Worker looked at issue and resolved it... Was configuration issue, grabbed new war file and put in a different folder...
I think that is very bad idea start inserting anything directly to APEX tables.
There is little change this might be your problem.