Unable to Upload Album in Photos

The first thing to try is to Repair the Library--close Photos and re-launch by option-command-clicking the app icon. You get a new dialog box (which seems often to hide itself behind other windows?) and you can OK the repair.

You can also try these things:

• Make a new user and see if the same problem recurs with it
• Use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens.
• Start in Safe Mode (different for different computers) This bypasses certain potentially disruptive processes.

           Start up your Mac in safe mode - Apple Support 

One of these steps may fix the problem, but their failure to work is also diagnostic.

Let us know if any of this helps...

iPhoto & Photos-- probably an OK thing. When the change occurred, we opened Photos for the first time and it converted the iPhoto library to the new, more complex and wonderful, Photos Library-- leaving the iPhoto library there, orphan like. So probably everything in the first is also in the second. iPhoto had "Events" rather than albums, and the conversion produced a folder labeled iPhotos Events, which I still have in my main Photos Library.

To repair the library, you first must close Photos. Then you (option-command) ⌥⌘-click on any of those things (Application icon, the Dock icon - even the Photos Library icon). Personally, I always ⌥⌘-click on the Photos Icon in the Dock, since it's right there. A window opens with this:

Like I said, this window, for some crazy reason, opens behind other windows. So you can click once on the Photos icon in the dock to switch to that window.

Good Luck!