I have the 2 above-mentioned bits and individually they work (ie Seedstudio ethernet shield (http://www.seeedstudio.com/depot/wiznet-ethernet-shield-w5100-p-518.html) on an Arduino board is OK, and ENC-based ethernet shield on shield adaptor (http://themakerspace.com/index.php?main_page=product_info&cPath=2&products_id=3) also OK). However when I place the Seeedstudio ethernet shield in the Picoduino shield adaptor the ethernet shield is in a constant state of reset (ie the RST LED is permanently lit), and obviously not usable in that state.
I'm guessing this is not a regularly used setup for most people, though if anyone can think why these wouldn't work together I'd love to hear it. What specifically would cause the ethernet shield to hold the reset state forever?
After I assembled the shield adaptor I double and triple checked for shorts etc. I'm a fairly decent solderer so I'm 100% certain I've not messed the board up (it's a very basic board to solder).