Sorry that there hasn't been much activity concerning your question. I am not 100% sure but I think that the Square is not compatible with the Nexus 7 at the moment. It might be a good idea to contact the developers of the app and reinforce the need. Again, I am not a user and am just going by what I believe I have read.
I hope that you are having a good experience with your Nexus and that this little bump in the road becomes smooth sailing in the near future.
Sent from my Nexus 7 using Tapatalk 2