Upload Progress Not Working

Once an uploaded is started, user sees the Upload Progress Box, but it never moves, stays at 0%. I can see using HTTP Live Headers that the browser is hitting the "FileVistaControl/filevista.asmx/GetUploadProgress" file every few seconds, but that page generates an ASP error...

equest format is unrecognized for URL unexpectedly ending in '/GetUploadProgress'.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: Request format is unrecognized for URL unexpectedly ending in '/GetUploadProgress'.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[InvalidOperationException: Request format is unrecognized for URL unexpectedly ending in '/GetUploadProgress'.]
   System.Web.Services.Protocols.WebServiceHandlerFactory.CoreGetHandler(Type type, HttpContext context, HttpRequest request, HttpResponse response) +493765
   System.Web.Services.Protocols.WebServiceHandlerFactory.GetHandler(HttpContext context, String verb, String url, String filePath) +361
   System.Web.HttpApplication.MapHttpHandler(HttpContext context, String requestType, VirtualPath path, String pathTranslated, Boolean useAppConfig) +577
   System.Web.MapHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +142
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +274


Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433

Please make sure that the web.config includes the following setting: 

<webServices> 
<protocols> 
<add name="HttpPost"/> 
</protocols> 
</webServices> 

Also see Problem Retrieving Language File for other possible reasons.