NullReferenceException when attempting to upload directory to S3 (.NET API - C#)

After scouring the web I am completely stuck on an application I am building to push directories up to Amazon S3 using C# (Targeting .NET 4.5). I am getting NullReferenceExceptions on the line of code that pushes the directory files using the UploadDirectory(TransferUtilityUploadDirectoryRequest) method of the TransferManager class. The problem is I cannot find anything that is null! The debugger doesn't show anything null either, so I'm obviously missing something here.

I read up that if you are uploading to buckets that have periods in them, you need to change the protocol to HTTP otherwise a NullReferenceException might be thrown, however I've done this as well and am continuing to receive the error, even when I created another bucket for testing that has no periods in it.

The portion of my code up to & including the line that causes the exception is below. The class called S3Info is just a helper class that I created that just stores some configuration info such as access/secret keys and other info:

public static void uploadDirectories(S3Info info, List<DirectoryInfo> dirs, Logger logger = null)
    {
        AmazonS3Config alterConfig = new AmazonS3Config();
        alterConfig.CommunicationProtocol = Protocol.HTTP;
        AmazonS3Client s3Client = new AmazonS3Client(info.getCredentials(), alterConfig);
        TransferUtility directoryTransferUtil = new TransferUtility(s3Client);
        TransferUtilityUploadDirectoryRequest uploadDirRequest;
        PutObjectRequest completeFileUploadRequest;
        uint uploadSuccessCount = 0;

        if (dirs == null || dirs.Count == 0)
        {
            logger.log("Nothing to upload.");
            return;
        }
        //upload directory with PDFs
        foreach (DirectoryInfo dir in dirs)
        {
            try
            {
                //configure upload request
                uploadDirRequest = new TransferUtilityUploadDirectoryRequest();
                uploadDirRequest.BucketName = info.selectedBucket.BucketName;
                uploadDirRequest.Directory = dir.FullName;
                uploadDirRequest.KeyPrefix = dir.Name + @"\";
                uploadDirRequest.SearchOption = SearchOption.TopDirectoryOnly;
                uploadDirRequest.SearchPattern = "*.pdf";
                uploadDirRequest.Timeout = 600000; //10 minutes

                //upload directory!
                directoryTransferUtil.UploadDirectory(uploadDirRequest); //exception thrown here

I'm a bit stuck at this point so I'm open to any suggestions the community can provide. Thanks.

EDIT: Stack Trace-

Object reference not set to an instance of an object. :    
at Amazon.S3.Transfer.Internal.UploadDirectoryCommand.Execute()

at Amazon.S3.Transfer.TransferUtility.UploadDirectory(TransferUtilityUploadDirectoryRequest request)

at S3Delivery.AmazonActions.uploadDirectories(S3Info info, List`1 dirs, Logger logger) in c:\Users\jblacker\Documents\Visual Studio 2012\Projects\S3Delivery\S3Delivery\AmazonActions.cs:line 173

Line 173 is the line referred to above.