Alpha problem on slice export

[timdw]

I'm having a problem with the slice/export tool. Everything works perfectly, apart from transparency. When transparency is selected, the whole image disappears - as if it's all becoming transparent! I've tried jiggling the Guides layer up and down, changing page colour, manually selecting the transparency colour, and GIF & PNG at 8 and 24bit. The resulting image if I do export is all white, but with the correct palette defined. I've attached a simple example, I'd be grateful if someone could take a look to see what they can see.

Thanks,

Tim