A few days ago I updated to WordPress 3.6. The last comment was before that date (on july the 30th).
Today I got a mail from a reader, that there is an error message after pre4ssing the „comment“-button.
I checked that and there it was:
„Invalid Data: Please go back and try again.“
After deactivating the plugin everything works fine.
I would be pleased if you can update the plugin.