This was a strange error with Magento18.104.22.168. I was in a product, trying to upload an image. The image would upload fine, but then error out with “Upload HTTP Error”. I changed permissions up and down the
/var directories and made them as loose with permissions as I could.
Still no change.
Then I happened upon this comment in the forums.
To anyone that has a HTTP upload error AND has a password protected store directory (for under construction reasons): remove the directory password protection and you’ll be able to upload your files again! That was what happened to me.