When you are uploading blobs from a stream using multiple roles (web or worker) to a single azure storage location it is possible that you may hit the following exception:
System.ArgumentException: Waithandle array may not be empty.
at Microsoft.WindowsAzure.StorageClient.CloudBlob.UploadFromStream(Stream source, BlobRequestOptions options)
at Contoso.Cloud.Integration.Azure.Services.Framework.Storage.ReliableCloudBlobStorage.UploadBlob(CloudBlob blob, Stream data, Boolean overwrite, String eTag)
The above issue is caused by a known issue, when utilizing parallel uploading for blobs in Storage API and it could occur in very rare occasion if conditions are matched for this issue to appear.
To solve this problem please disable parallel upload feature by setting as below: CloudBlobClient.ParallelOperationThreadCount=1