Unable to upload images to new listing. Any helpers?

Hi All. Have created a new listing this evening but for some reason when I try to upload the image, a ‘Network Error’ message in small red writing appears underneath the upload square where the image should go. Have checked all the obvious such as network connection, image pixel sizes, etc. but to no avail. I’ve created hundreds of listings in the past but have never come across this one. Any advice or ideas are more than welcome.