Board Thread:Support Requests - Getting Started/@comment-31146746-20170723153909/@comment-28587411-20170724155830

It's possible that the image you are trying to upload has already been uploaded, and is protected. Try uploading the same image under a different name.

If that doesn't fix your problem, go to Special:Images (on the wiki you're editing of course) and try uploading your image there first, before you edit the article to add it. Then, you can use that image right off of the wiki instead of uploading it in the middle of editing.