I'm sorry, at this point, I've still been unable to replicate this error such that I can resolve it. Often, it can be a matter of simply trying to activate the plugin again to fix. Alternately, trying disabling your other plugins, activating this one, and then activating the others again to get around.
If you can help me with how you fix the problem by leaving comments below, hopefully a clue will present itself for a future fix.
- Attempt to activate again via WordPress Admin > Plugins, Activate link
- Delete the plugin and install again via WordPress Admin > Plugins, New and then attempt to activate via WordPress Admin > Plugins, Activate link