Why would a TextBlock with DropShadowEffect show a solid black background on one XP machine?

We have a WPF application in which we have the following XAML:

<TextBlock x:Name="HeaderRightSubtitle"
        HorizontalAlignment="Left"
        VerticalAlignment="top"
        FontSize="10"
        Foreground="#FFFFFF">
        <TextBlock.Effect>
            <DropShadowEffect
                Color="#FFCACACA"
                ShadowDepth="1"
                Opacity="100"
                RenderingBias="Quality"/>
        </TextBlock.Effect>
</TextBlock>

It shows a nice shadow on all machines (XP, Vista) except for one XP machine on which is shows the white text on a solid, back, rectangle background also a bit offset. The XP has the same theme as the other machines.

Has anyone experien开发者_开发百科ced this? What could be causing the DropShadowEffect to produce a solid black background on this one machine?

Check the version of .Net installed on the XP Machine. You might be missing SP2 for 3.0 or SP1 for 3.5.

What video card is in the machine and are you using the latest version of drivers? Also, what version of DirectX is installed? If I had to guess, it's something with the card/drivers.

I've had this problem too. It was due to an old nVidia card (FX5200 if I remember correctly). After extensive research I finally found out that nVidia fixed the bug in a newer driver, but that driver wasn't provided for the video card, because it was too old (legacy). So the only options were to either not use DropShadowEffect or buy a new card.