Problem getting Office Web App 2013 to work with SharePoint 2013

I have installed an Office Web Apps 2013 Server following this document -> http://technet.microsoft.com/en-us/library/jj219455.aspx

After the installation, I am running this command -> New-SPWOPIBinding -ServerName <ServerName> -AllowHTTP, but get the following error:

New-SPWOPIBinding : New-SPWOPIBinding is unable to add the requested WOPI
bindings because the provided XML is invalid.
At line:1 char:1
+ New-SPWOPIBinding -ServerName <ServerName> -AllowHTTP
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (Microsoft.Share...tNewWOPIBinding:
   SPCmdletNewWOPIBinding) [New-SPWOPIBinding], SPCmdletException
    + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletNewWOPIB
   inding

Have I missed something?