Why am I getting these error messages all of a sudden?
How big is the image you are trying to upload? This error can occur if the file is too big. Check your php settings on the server (upload_max_filesize and post_max_size) in php.ini.
Alternatively you can upload the image to application/files/incoming (for example via FTP) and then select it in the upload prompt (there is a tab called "incoming"). Or you simply scale down the image before uploading.