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.

This update thingy is causing havoc for lots of people at the moment. We don't work for LW & can't explain why these update prompts have suddenly started. You may or may not be able to redownload Pro, depending on when you bought the app & who you bought it from. Read the post below & see if that makes things any clearer.
ATTENTION: LW Pro users!! Update info!!

You could try posting at this other forum & see if any of the LW developers can shed some light on the situation.
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If you lost everything in your library, I'd say that your saved folder had been changed from the default location. By default, Windows users' files are saved to C:\Documents and Settings\username\Shared. This is a safe location & saved files won't be effected if LW is removed If people aren't careful with where they save to (eg saving to somewhere within LW's program files) then they stand the chance of losing their files if LW's removed.