I'm not seeing the improperly encoded message when opening that page or the server behavior for insert on it. What would I have to do to reproduce it?
The code on the page you sent looks perfectly good. The errors you are getting are server configuration issues that have nothing to do with your code.
The error message says:
That is the problem. It looks like you are using a folder with a dollar sign in it as the session save path. That might be the problem... or it could be the permissions on that folder. Either way this is something that you will have to resolve on the server. You may want to open a trouble ticket with your hosting provider to help.
If you provide steps to reproduce the error with the Uploaded file name field then I can look into that one and make sure it gets fixed.