concurrency on ExecuteNonQuery

Prob: I am updating the table... while updating i stopped in middle before update the query. And i opened sqlplus and updated the same value that i am updating from .net and commited in sqlplus, and afterwards i started working from the samepoint on .net and i am not able to throw exception instead it is updating the value.. But i want to throw exception.

Please help me out of this problem as i need it urgently...

Regards

shravan kumar J