Exception while calling EncryptionSDK.Encrypt

Hi Experts, I am a beginner and trying create a small sample application for encryption and decryption. I have used the sample code provided with documentation. But getting an error while running the application as "Unexpected Exception from aws KeyManagement Service : The service returned an error. See inner exception for details ( and there is nothing in inner exception)

I am using C# and AWS.EncryptionSDK

Any help is appreciated.

Regards, Nidheesh