If you have obtained any of my premium add-ons from another site, you DO NOT have a valid license for those add-ons and no support will be given to you. The only place that can sell licenses for my premium add-ons is this site.
Please copy and paste the error from the admin area here. The screenshot does not allow me to see the entire line of some of the trace information.
But if I had to guess, I would guess that you don't have the PC sender name set to a valid user for your form. So far as the multiple submissions, it could be people trying to submit the form multiple times after they get the error message.