Not sure what's wrong. I just ran a test post for my car and all was good. Both the "Attach File" tab and the drag and drop a picture file worked for me and it posted fine. Make sure you have filled out all the fields and the listing type at the end.... That's all I got. If it's still giving you grief, maybe @Nik has a way of seeing what you are doing wrong...
As per @Rruuff Day hit the attach files button under the main listing description box and add your pics. I'm not seeing any issues on the backend. Let me know if you're still having issues.