I'm not sure what instigated the situation, but I think I can describe how it happened.
I changed an option in the widget. I think I cleared the title checkbox, but I'm not certain. After saving, wordpress wouldn't display pages. I was too sleepy to capture the error so I deleted the plugin directory and wp was restored to normal function.
A day or two later, I tried reinstalling the plugin and this error resulted. I was able to work around by going into the database and delete the widget. Hopefully your fix will prevent it from happening in the future.
I'm going to investigate how I made it happen to see if I can reproduce the root cause, but you may want to take a look at what happens when you clear the title checkbox. I'm not certain that's what I did, but I think it's the most likely candidate.