Error uploading large videos

Hi! I installed a plugin called “Add from server”. I moved my videos to the proper folder wp-content/uploads/2015/09, however upon pressing the upload button, All it says is “are you sure you want to do this?” and the only clickable button is “Please try again.”

I’ve tried a dozen times and still it isn’t uploading. Please reply ASAP because I’m on a very tight deadline. THANK YOUUUU!