Hay, This happend to me On 2 WP sites in same time. This happend due to 2 things for me
1st Check your wp-inclues dir for correct version(i’ve accedently upload 2 versions for one of my blogs, funny ha)
if not that the common one is your browser security, try firefox, editor will work firefox if not working on IE so this issues is not on your upload it’s on browser issue
