AWS Polly c# windows app error connecting to Amazon polly servers

simple c# windows app is written using current AWSSDK.CORE and AWSSDK.POLLY that converts text to mp3 file. app works ok on some computer but it give error connecting AWS polly server connection exception on specific windows computer in the cloud running windows 7 profession. when app debugged on the computer where it gives exception while retrieving voices list DescribeVoicesResponse describeVoicesResponse = amazonPollyClient.DescribeVoices(describeVoicesRequest); it shows exception message message : "Unable to connect to the remote server" status is : ConnectFailure Inner exception value is inner exception : {"A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 'IP Address here::443'"} I even tried by turning off firewall during debugging but still it gives ConnectFailure . what steps/configuration changes is required to resolve connection failure error .