There's a couple of reference to that error.
Open your applications folder. Do you have a folder created called "form" in there?
Can you paste the last part of the url you see when choosing the upgrade option? What's set for the "appKey" parameter?
If your database table has an entry, check if there are any cache issues. See ACP > System tab > Support > " Something isn't working correctly. ". See if your getting any errors rebuilding your cache, it might be that an app is preventing the application cache rebuilding.