Looking at it, there are two important layers. A casting failure page and a casting progress page. The easiest thing to do would be to reverse the order in which these pages appear in the stack. This way when the progress bar is visible, it covers the failure message instead of the current opposite.
Current XML layout:
Code:
<Page Name="Casting">
<Page Name="CastingFailure">...</Page>
<Page Name="CastingProgress"><Text Name="SpellName" /><Page Name="Progress">...</Page></Page>
<Page Name="WindowFrame">...</Page>
</Page>
Desired XML layout:
Code:
<Page Name="Casting">
<Page Name="CastingProgress"><Text Name="SpellName" /><Page Name="Progress">...</Page></Page>
<Page Name="CastingFailure">...</Page>
<Page Name="WindowFrame">...</Page>
</Page>
This would be easier than say adding scripts to the OnShow/OnHide events of the two pages so that only one was visible at a time.