I see “ERROR: posting to Smush.it” message for many images in the Media Library list (without debug set in Settings). With debug mode on, attempted to upload image & get “ERROR: [filename] An error occurred in the upload. Please try again later.”
Same as above,the image appears to have been uploaded (thumbnail shows in Media Library) but can’t add it to page unless closing out and trying again. Images that are already uploaded do seem to smush OK when it’s done one by one within the Media Library.
Smush.it plugin Version 1.6.5.4 w/ WordPress 3.6.1