aws sdk for .net ec2 "Unable to reach credentials server"

I have installed the AWS SDK for .Net.

I need to write a program to change the permissions for a security group, and I found an example of how to do this in C# on http://ift.tt/1zWkjgA (page 39).

Dim ipPermission As New IpPermission()
            ipPermission.IpProtocol = "tcp"
            ipPermission.FromPort = 3389
            ipPermission.ToPort = 3389
            ipPermission.IpRanges = IPRange

            Dim ingressRequest As New AuthorizeSecurityGroupIngressRequest()
            ingressRequest.GroupId = "sg-xxxxxxxx"
            ingressRequest.IpPermissions.Add(ipPermission)


            Dim endpoint As RegionEndpoint = RegionEndpoint.EUWest1
            config.RegionEndpoint = endpoint
                         Dim ec2Client As New AmazonEC2Client(credentials, config)
            Dim ingressResponse As System.Threading.Tasks.Task(Of AuthorizeSecurityGroupIngressResponse) = ec2Client.AuthorizeSecurityGroupIngressAsync(ingressRequest)

However, when I try to run the code it comes up with the following exception:

Unable to reach credentials server

Is this a bug in the SDK, or am I doing something wrong?

I have tried everything that I can think of and nothing is helping, and I'm desperate for help!