Proxy Option Greyed Out / Sequence Turns Red

Hi, 

I'm working on a project where I need to put a series of images downloaded from Unsplash and Pexels on the timeline.

I added a voice over, music and video file prior to adding the images and they work perfectly well (timeline has the yellow bar). However, when I add an image, the sequence turns red. I added all my images and rendered the timeline. Still, every single change I make turns the sequence red again - even if it is just adjusting the scale. Frequently, when I try to render, it crashes Premiere Pro.

To fix this,  I decided to create proxies. I tried to create them with the images still in the timeline but the option was greyed out. To combat this, I deleted the images and tried to create the proxies from the project bin - it was still greyed out.

Does anyone know why either the sequence turns read or the proxy option is greyed out? Any help would be much appreciated.

Thanks