You may not have done anything wrong, I made an entry and the screen titled Your Home Energy Credit Summary did show Your Home Energy Credit "0", but when I went back out to Deductions & Credits, the correct 10% of the amount I had entered for the cost was reflected in Home Energy Credit.
So you might want to check and maybe it will be there even though it showed "0" on the other screen.
Just a note, the cost of the insulation is deductible, and not the installation.