No material selected No material selected!

I can not download the code for my parts, I do keep getting an note ate the top thats says " no material selected". but I did select my material MDF and the sheet size 8’ x 4’. When I try to download my code nothing happens. can anyone help?

I found that the material selection MDF does not work. If I select “Plywood” I don’t get the error and am able to download a file… but the file it downloads is a .TXT file… Why is this?