Adding images to photo album

For years I’m using RW for my site. Not much changed the last year and everything was working fine. Since december 2015 I’m having troubles adding pictures via media. Most of the pictures don’t have troubles but some pictures generate a popup with “Failure to add images” further no commend exept the image name example DSC0123.jpg. I used the rejected images before with no problem. I can’t find any solution on the internet