I had a pretty up to date version of Limewire Pro...4.14 or so...all paid for and working just fine...but I too succumbed to the update nagger.. and I had the same thing happen...lost all my downloads, everything in my library ..I went through the same as you with error messages.. I finally downloaded an earlier version of pro.. 4.12.6..but what I finally got was NOT the PRO version 4.14.10
When I tried to log in to upgrade through Limewire, I get a message telling my e mail address doesn't exist. I only ever use two and I tried both and both were rejected. I feel a little ripped off because now I will have to PAY for a new Limewire Pro unless I can somehow retrieve my information from Limewire. They seem unreachable and untouchable.