Hi Subbu,
As far as BO security level is concerned it fine.I have given power user role to this user from CMC and then tested.Still the same issue.But for BW access ,security team says they checked and replicated the access same as other user(who is not getting this error)..Even i guess some roles are missing from BW side.
Let me try creating a new report using the same Bex connection/Query using that user's id.