error deleting user

Hi,

I'm trying to delete a user and I always get this error:

"com.sap.security.core.persistence.datasource.PersistenceException: Principal "UACC.company.user_xxx" is not deletable."

The code I use is this:

IUserFactory userFactory = UMFactory.getUserFactory();

userFactory.deleteUser(userUniqueID);

This user was not created via SAP.

I don't know if this has some influence in this situation.

Thanks for any help conceeded