NotAuthorizedException while uploading image to Amazon S3

While trying to upload image to amazon s3 using,

AWSS3TransferManager.defaultS3TransferManager().upload(uploadRequest).continueWithBlock{...}

Getting log in verbose mode,

AWSiOSSDKv2 [Debug] AWSURLResponseSerialization.m line:82 | [AWSJSONResponseSerializer responseObjectForResponse:originalRequest:currentRequest:data:error:] | Response header: [{ "Content-Length" = 129; "Content-Type" = "application/x-amz-json-1.1"; Date = "Sun, 30 Aug 2015 04:54:14 GMT"; nnCoection = close; "x-amzn-ErrorMessage" = "Access to Identity 'us-east-1:9b28176f-XXXX-XXXX-82d6-f64569ae14ce' is forbidden."; "x-amzn-ErrorType" = "NotAuthorizedException:"; "x-amzn-RequestId" = "2a1fc807-4ed3-11e5-a8b0-9368dcfb1138"; }]

I have confirmed bucket access policy to have proper access. What would be possible reason for such error?