First try the browseruploader instead of the flashuploader
if you see at media-new.php a blank screen this solution will do the trick with v4.5.2
Step-by-step guide
1. backup plugin folder and remove all plugins from server
2. use a standard theme like Twenty X
3. go to dashboard > updates > reinstall this version of WP
4. upload and activate all plugins again
5. use any theme you want
Try first the basic web uploader
This will fix HTTP error on image upload.
