For some dumb reason I am also having this same issue today on my new Lumia 920. I have been able to upload screenshots to FB a few times before today but not now. I am getting this error: "We can't upload your picture right now" and also seeing "Can't download tags right now." I was able to upload a photo from another folder. Wonder what's going on?
Earlier today I updated to the most recent version of FB Beta. I figured that was the issue so I uninstalled it, tried a soft reset, and later installed the new Facebook version 5 just updated in the store. Nothing worked. Screenshots are still failing.
Hope it's just a glitch. I'll try again tomorrow.