I have been paying for the license for some time now. I lost my license file and wanted to re download it.
BUt when I went to the store, my downloads is empty
Please read Ashleys post above yours.
You should email for all licensing issues.
BTW you look like you were an early adopter - like me - so we don't actually have a purchasing history as we got ours before the store existed.
You should still have the email with the key attached, however, but if not, then email support.