Those log messages are saying no file was posted, those are INFO logs not ERROR. Are you sure those specific errors correlate to actual upload attempts and not some web bot poking at the upload url?
What feature are you trying to upload files in?
If you use web browser tools do you see any script errors in the script console on the page where you are trying to upload? Possibly a script error on the apge is preventing it from posting the files.
Also if you upgraded then NeatUpload dlls are still in the /bin folder, make sure there is nothing in Web.config that is enabling NeatUpload. We removed all references to it from our web.config so its important to use the new Web.config and not try to keep an old one that may still reference NeatUpload. Wouldn't be a bad idea to delete the NeatUpload dlls also.
You've got some other errors about appKeepalive which I recommend that you disable, especially since the error indicates it isn't working.