Kate - Paint and varnish remover is the only thing I can think of.
Whoever painted it - shouldn't have - grasscloth is really easy to remove otherwise.
You could try a wallpaper remover - but you are going to have to score it with a Paper Tiger.......even then...I am not sure......
I am sure it will be difficult and messy......
Sorry I don't have an easy answer for you.. :>(
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