Guide Not Allowing Me to Add Images

Hi there! 

I am attempting to upload images to an article in guide, and it will only let me upload one, and then it will not allow me to upload anymore. I tried JPEG and PNG, but neither are successful when adding any additional images besides one. 

Can you please help? In the image below, it will only allow me to add/select SignInScreen.jpeg, but it won't allow me to select the other one in either JPEG 
or PNG.