Photos greyed out for selection to upload to website

I am having trouble uploading some of my photos from my Mac to a website. When I navigate to my photos from the website to select which photos to upload, some of the photos are "greyed out" (very random which ones are and which aren't). If they are greyed out I can't select them. If I access them directly from my iPhotos library or from my desktop they appear normal and accessible. Included a screenshot of how they appear