Tried to take a privilege away from a user, but it failed with ORA-01952.
SQL> revoke create table from hr;
revoke create table from hr
ERROR at line 1:
ORA-01952: system privileges not granted to 'HR'
ORA-01952 means that the system privilege you want to remove from a user has never been granted to it. That's why the statement failed. You can ignore it if you have known the whole truth.
Most likely, you may misunderstand the situation. For example, a user who already has some tables, and we naturally assume that it has CREATE TABLE privilege. When we tried to revoke the privilege from the user, we got ORA-01952.
The truth is, those tables were created by other user who has CREATE ANY TABLE privilege. In other words, the user does own some tables, but which were created by someone else.
Another misunderstanding is that, you thought that you have granted the privileges properly, but actually no.