Why can't I upload photos to online site?

I'm having trouble uploading photos to an online site. I've contacted the site, but no-one else is having this problem, so I think it's my computer. Their specific upload module must be used on this site. It takes me to my files where all the .jpg files are grayed out. I've tried other file types and they come up also grayed. I've used this procedure many time before and never had a problem. I can physically move photos from my computer to other sites without problem, but this site has it's own module. I've seen this subject here before and I tried the answer outlined below. It made no difference. Can you help?

may be corrupted Finder preferences ..

Open the Finder. From the Finder menu bar click Go > Go to Folder

Type or copy paste the following:

~/Library/Preferences/com.apple.finder.plist

Click Go then move the com.apple.finder.plist file to the Trash

Now try uploading photos.

Please help if you can. Thank you.