Fix MRP Runtime error

The site is mrpworkshop.com and the error is in https://mrplanning.clientserviceportal.net. My client is getting this attached error message whenever she tries to upload a pdf into the system. It's something she's done successfully 100 times before. As of yesterday morning, for no apparent reason, it started giving her that error every time she tries it. Can you help with that? What would you need to get that working again? We're in a huge hurry since they can't move projects forward without being able to upload pdf's. This is not a long term project. I hope it takes less than an hour to fix.