Unable to mark ad as active as you have not uploaded any valid images. Setting ad as pending.

I upload image, image appears in "image" section (is a .jpg file), but, when I try to "active" it (in "status" section), system returns:

"Unable to mark ad as active as you have not uploaded any valid images. Setting ad as pending."

PS: same error occurs with ad-5.x-1.0-beta8 version.