Cannot upload images in auction listings

I have just installed the latest responsive auctions theme on my website at https://ehangar.com/auctions

Within the Admin panel, when I add a new listing: In the Add Listing page, under the Attachments section, I click on the Choose File button and select the files I want to display. When I click the Save Changes button, the page refreshes and when I look at the Attachments section, it show “No file chosen” and no images appear in my listing.

When I use the Attachments Manager, after uploading, I get the “Error: Empty file upload result” messages for all the image files I wanted to upload. Please see screenshot of this.

Right now, the only way I can add images to my listing is via the Add Media button.

Strangely enough, listing and adding images using the front-end interface as an “ordinary” member works!

Why doesn’t it work when posting listings as an Admin in the admin panel?