Firstly, my impression was that you couldn't put apps on your SD Card.
So only things I can think of is -
1) Either it downloads extra files and saves them on your SD Card. And it needs that space.
2) It downloads extra files and saves them on your Nook. But it is used to Android and gives SD Card message.
Perhaps it's using the standard Android message which doesn't match on Nook.
Try the following:
1) Archive some apps that you aren't using so there's 1.6 GB of free space on your Nook.
2) Clear up 1.6 GB of space on your SD card. If you don't have an SD Card then skip this.
3) restart your Nook.
4) Now try the install.
Note: If it doesn't work then you could buy a SD Card and try. You can get a 4 GB one for under $10.
Downlaoded it last night. Took a loooooonnngg time, but it was successful.
Plays really well. I had read the problems others had and took a gamble. I did have an SD card in there, but did not do anything special