@beckywc - I would say there was a problem migrating your previous lists. Did you restart calibre after installing the new version?
Can you please attach your Reading List.json file to a post (you may have to zip it first to attach it, or else just paste the content into a spoiler tag on here). You can find this using Preferences->Misc->Open Calibre configuration directory and going to the plugins subfolder.
If you just want to get going, you could just delete this file and restart calibre, but that will lose your lists.