The next thing I'll try on your server is put the AVFP demo app in a separate App Pool from yours to separate it from whatever it is you're doing that corrupts the system.
You need to isolate exactly what is causing the problem. You'll help everyone by doing this. You can do an IISRESET from the command line (as Administrator) to reset it back to normal or Recycle the App Pool from the IIS Manager. Start by doing a simple JSON return from a query like the GetEmployees example method. Just do that over and over to see if you get the message. You probably won't. Now try some of the other code in your app. Somewhere in there you are doing something to cause this, I'm pretty sure.
I just don't have the time to debug your application for you. You need to help all of us by figuring it out and doing your part. After that, if it's feasible, I can put something in there to prevent this sort of problem from happening automatically. An Error method in your Controller class might help with the COMRETURNERROR command.
You need to isolate exactly what is causing the problem. You'll help everyone by doing this. You can do an IISRESET from the command line (as Administrator) to reset it back to normal or Recycle the App Pool from the IIS Manager. Start by doing a simple JSON return from a query like the GetEmployees example method. Just do that over and over to see if you get the message. You probably won't. Now try some of the other code in your app. Somewhere in there you are doing something to cause this, I'm pretty sure.
I just don't have the time to debug your application for you. You need to help all of us by figuring it out and doing your part. After that, if it's feasible, I can put something in there to prevent this sort of problem from happening automatically. An Error method in your Controller class might help with the COMRETURNERROR command.