Sorry, but in this case you're out of luck.

2 years ago, buying Pro entitled you to free updates & email support for 6 months. So you would've been able to download Pro for free, for 6 months after your purchase. There's a 12 month option now, but that definitely wasn't available 2 years ago. Whatever versions of LW you download while your Pro privileges are current are yours to use for as long as you like. But it's up to the user to save & back up Pro installers

Once your Pro privileges have expired, your email address won't be in LW's database anymore - that's why your email address isn't being recognised.

Did you buy Pro from the official site Lime Wire » Download LimeWire ?
Some sites offer 'unlimited' or 'lifetime' deals, but they're just scams.