cannot see the image in run-time (wpf button)

hi all of you,

How odd! In design-time I see the image inside the button but when I run my app button appears wihtout it..

I've tested on PNG files too unsuccesfully...

[...]

<Button Margin="20,285,0,0" VerticalAlignment="Top" Width="75" Height="30" >
<Image Source="Imagenes/email_a.jpg" />
</Button>
</Grid>

</Page>

TIA,

Enric