I was on v1.9.19 but GumRoad sent me a notice to update the plugin. I grabbed v1.9.28 from them but once I installed, I get the above error when trying to Add or Edit a new Flipbook, thus rendering the plugin useless. The front end doesn't work either.
Help?
Need access to your WP, write me email author@3dflipbook.net
Nevermind - I figured out that I had to delete the entire old plugin directory before uploading this latest version of the plugin.