Tooltip: "Only one root element is allowed" error

I have added a Content\Tooltip to the MenuSubItem. I've set the Trigger to Hover. When I hover over the menu item it blinks a small arrow, but does not show the Tooltip. In Edge and IE I get: "XML5632: Only one root element is allowed." Chrome does not have the error, but it doesn't show the Tooltip either.

Any thoughts?

Nélio Dionisio wrote:

Hi :)

Check this post: 

Hope it helps,

Joao suggests that this error has no effect on the application. It definitely has an effect on mine. The Tooltip does not show and the error repeats every time the tootip should appear. Although the error is not recorded in Chrome, the tooltip does not show there either.