Hi Ashok,
Looks like a problem in the tested application, actually - it's hard to imagine how TestComplete can affect its DB connection. Are you sure the same version of the same application will work correctly in the same scenario, but on another machine, where TestComplete is not installed? Also, the error message seems to be a custom one, so could you please ask your developers to share some internal details on the original exception which causes this? The "unable to connect" string might denote too many things - starting with network cable unplugged and ending with a broken data provider installation or wrong connection string.
