It should be a problem with AWS credentials. Create a credentials file at any path where you want to access this path from the web service application. Make sure not to include any extensions. The credentials file should contain only the below data:
After this you need to set the path in app settings in the Web.config file:
<add key="AWSProfilesLocation" value="C:\awsfile\credentials" />
<add key="AWSRegion" value="us-east-1" />
Hope this helped!