EBS R12.1.3 : Creating users using external identiy management

Hi,
We are using TIVOLI identity manager.     We are trying to create users in EBS R12.1.3.   While creating we are having the following issue.

CTGIMT007E A system error occurred while adding an account. The account is not added.

Error: ERROR: java.sql.SQLException: ORA-20001: APP-FND-02600: Unable to create user UGOPAJU123 due to the following reason(s): This user name is already in use. Please enter a unique user name.. ORA-06512: at "APPS.APP_EXCEPTION", line 72 ORA-06512: at "APPS.FND_USER_PKG", line 1150 ORA-06512: at "APPS.FND_USER_PKG", line 1196 ORA-06512: at "APPS.FND_USER_PKG", line 1315 ORA-06512: at line 1