Office Web Apps 2013: The HTTP service located at... is unavailable.

Problem

You install updates to the (single) Office Web Apps Server 2013.  You then log into and execute Get-OfficeWebAppsMachine on this server and see the following error:

Get-OfficeWebAppsMachine : The HTTP service located at 

http://[yourOWAserver]/farmstatemanager/FarmStateManager.svc
is unavailable.  This could be because the service is too busy or because 

no endpoint was found listening at the specified address. Please ensure 

that the address is correct and try accessing the service again later.
At line:1 char:1
+ Get-OfficeWebAppsMachine
+ ~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Get-OfficeWebAppsMachine], 

ServerTooBusyException
    + FullyQualifiedErrorId : System.ServiceModel.ServerTooBusyException,

Microsoft.Office.Web.Apps.Administration.GetM   achineCommand

You check Services and find that the Office Web Apps and World Wide Web Publishing services are in the Running state. You then check IIS and find that all application pools and sites have Started status.

Solution

• In IIS, stop and start the HTTP80 site.

Notes

• Don't yet understand why, but this worked.