Hi Pradeep,
One quick workaround here might be trying to request reports with shorter period of time and/or imposing some constraints, e.g., campaigns with only STATUS=ENABLED.
If you can get reports without any errors, it might be possible that your account is so large that there were problems getting your report.
As I have no information about your account and numbers of campaigns, it's hard to give you a very specific answer.
If you would like me to investigate further, could you please send me more information about your account?
To do so, please click Reply privately to author and send me your clientCustomerID, types of reports you requested, and if possible, the SOAP logs you requested to the API server.
(Please do not post your private information here)
Cheers,
Thanet, AdWords API Support