I don't have an answer, just wanted to share your frustration. I'm running Windows Vista on a Toshiba Satellite with 40+GB free hard disk space and 2GB RAM so space is not the problem. All updates have been made.
My AIR log shows the identical error info. I have requested help from the application's author, which first suggested it was Firefox causing the problem, but downloading from Chrome and IE made no difference. Nor did reinstalling AIR. A friend was able to download this app with no problem. And I was able to download the other (somewhat smaller) JL app with no problem, which really seems strange.
Hoping someone here with more tech knowledge might be able to offer a suggestion. If I get a helpful reply from the app author, I'll be sure to share it.