I have a customer that was experiencing that for some users the SPEAK upload dialog would hang (well was not finished after 30 minutes). It would appear that the image had been uploaded (see below) but it never finished.

After some investigation I found that the users did not have access (create, write or delete) to the media root folder, but the strange thing is that the item was created, but the blob field was empty?

With a lot editors around the world soon the root folder was full of items without images, when I checked the log I could see that in fact a System.UnauthorizedAccessException was being cast (see complete exception below) but not because the item could not be created, but because it was not possible to write to the item?

The user did not have the create permission, so why was the item created? And why does the upload dialog not warn about the user they can not create and or write to an item? so I reported this to Sitecore and they have registered it as a bug and the following hot fix is available:

Sitecore CMS 7.5 rev. 141003 Hotfix 431794-1

If you don’t want to install a support DLL and JavaScript an alternative workaround is to  switch to the non-SPEAK version of the Select Media dialog by performing the following steps:

1. Edit the /App_Config/Include/Sitecore.Speak.Applications.config file;
2. Comment out the following lines:

   <overrideXmlControls>
      <override xmlControl="Sitecore.Shell.Applications.Media.MediaBrowser" with="/sitecore/client/applications/Dialogs/SelectMediaDialog" />
   </overrideXmlControls>

Complete Exception

Exception: System.Web.HttpUnhandledException
Message: An unhandled exception occurred.
Source: Sitecore.Mvc
   at Sitecore.Mvc.Pipelines.MvcEvents.Exception.ShowAspNetErrorMessage.ShowErrorMessage(ExceptionContext exceptionContext, ExceptionArgs args)
   at Sitecore.Mvc.Pipelines.MvcEvents.Exception.ShowAspNetErrorMessage.Process(ExceptionArgs args)
   at (Object , Object[] )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
   at Sitecore.Mvc.Filters.PipelineBasedRequestFilter.OnException(ExceptionContext exceptionContext)
   at System.Web.Mvc.ControllerActionInvoker.InvokeExceptionFilters(ControllerContext controllerContext, IList`1 filters, Exception exception)
   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
   at Sitecore.Mvc.Controllers.SitecoreActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
   at System.Web.Mvc.Controller.<>c__DisplayClass22.<BeginExecuteCore>b__1e()
   at System.Web.Mvc.Async.AsyncResultWrapper.<.cctor>b__0(IAsyncResult asyncResult, Action action)
   at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult)
   at System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
   at Sitecore.Mvc.Routing.RouteHttpHandler.EndProcessRequest(IAsyncResult result)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
Nested Exception
Exception: System.UnauthorizedAccessException
Message: The current user does not have write access to this item. User: XXX\yyy, Item: Desert ({B1793B35-A61D-40AC-869F-4AD66A752234})
Source: Sitecore.Kernel
   at Sitecore.Data.Items.ItemEditing.BeginEdit()
   at Sitecore.Resources.Media.MediaData.SetBlobStream(MediaStream mediaStream)
   at Sitecore.Resources.Media.Media.SetStream(MediaStream mediaStream)
   at Sitecore.Resources.Media.MediaCreator.AttachStreamToMediaItem(Stream stream, String itemPath, String fileName, MediaCreatorOptions options)
   at Sitecore.Resources.Media.MediaCreator.CreateFromStream(Stream stream, String filePath, MediaCreatorOptions options)
   at Sitecore.Controllers.MediaController.Upload(String database, String destinationUrl)
   at lambda_method(Closure , ControllerBase , Object[] )
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)