CiscoIPPhoneImageFile not working on 8800 series phones

I'm using the Idle URL, set the timer for 10 seconds and the Phone displays "XML error [4]: Parse error

I can't find anything recent on it, but older posts point to the image size being to big for the phone service. I have reduced down to 400x200 (background image for the 8841 is 800x480).

Does anyone have any experience using the Idle URL to display an image on 8800 series phones? is this the right XML format?

<CiscoIPPhoneImageFile>

  <Title>Cisco Live</Title>

  <Prompt>Cisco Live</Prompt>

  <LocationX>-1</LocationX>

  <LocationY>-1</LocationY>

  <URL>http://10.1.58.50/CiscoLive.png</URL>

</CiscoIPPhoneImageFile>

The XML looks good, however per the '9.1.1 and Later...' developer notes document, the target resolution is 559 x 265:

https://developer.cisco.com/site/ip-phone-services/documents/

See the 'CiscoIPPhoneImageFile' section for other technical details about supported image files.