Some more information might help here.
Can your Avoca actually 'see' your router? (i.e. is it listed as an available connection?). What happens when you try to connect to it? Do you get the opportunity to enter your router's pass key? Are you sure that you're actually entering the correct key? Have you tried connecting to the internet at a different location (e.g. using the free wi-fi in a Wetherspoon's pub or Tesco Extra?).
What size SD card are you trying to use? (Some devices won't work with cards beyond a certain maximum capacity).
Have you tried asking Avoca for help?
http://www.avocasupport.com/contacts/