Photoworks:where's my glass gone?

aaaarrrrrggggghhhhh

SW2006 SP1

Photoworks: Indirect Illumination (minimum as I dont have all year) Memory management ticked, highest anti alias, no lights - just indirect lighting

I have a scene with a bottle in it, using 'white glass' but changed to a green colour. I render in preview and it's fine (great in fact) and then I send it to render to file quite big and it's fine, then I send it to render at 4000pixels across and it takes four hours and I come back and MY GLASSS HAS BECOME A SILOUHETTE OF SMALL GREY SQUARES.

How do I explaing this to the client who wants the visual?????

Can anyone help me get my glas back, even if it means re-rendering?

Thanks