Photos was unable to repair permissions on your library.

Back up all data before proceeding.

This procedure will unlock all your user files (not system files) and reset their ownership, permissions, and access controls to the default. If you've intentionally set special values for those attributes on any of your files, they will be reverted. In that case, either stop here, or be prepared to recreate the settings if necessary. Do so only after verifying that those settings didn't cause the problem. If none of this is meaningful to you, you don't need to worry about it, but you do need to follow the instructions below.

Step 1

If you have more than one user, and the one in question is not an administrator, then go to Step 2.

Triple-click anywhere in the following line on this page to select it:

sudo find ~ $TMPDIR.. -exec chflags -h nouchg,nouappnd,noschg,nosappnd {} + -exec chown -h $UID {} + -exec chmod +rw {} + -exec chmod -h -N {} + -type d -exec chmod -h +x {} + 2>&-

Copy the selected text to the Clipboard by pressing the key combination command-C.

Launch the built-in Terminal application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Paste into the Terminal window by pressing command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.

You'll be prompted for your login password, which won't be displayed when you type it. Type carefully and then press return. You may get a one-time warning to be careful. If you don’t have a login password, you’ll need to set one before you can run the command. If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator.

The command may take several minutes to run, depending on how many files you have. Wait for a new line ending in a dollar sign ($) to appear, then quit Terminal.

Step 2 (optional)

Take this step only if you have trouble with Step 1, if you prefer not to take it, or if it doesn't solve the problem.

Start up in Recovery mode. When the OS X Utilities screen appears, select

Utilities ▹ Terminal

from the menu bar. A Terminal window will open. In that window, type this:

resetp

Press the tab key. The partial command you typed will automatically be completed to this:

resetpassword

Press return. A Reset Password window will open. You’re not going to reset a password.

Select your startup volume ("Macintosh HD," unless you gave it a different name) if not already selected.

Select your username from the menu labeled Select the user account if not already selected.

Under Reset Home Directory Permissions and ACLs, click the Reset button.

Select

 ▹ Restart

from the menu bar.

is there not a simpler way to do this?

No. Click the Support link at the top of this page, or make a "Genius" appointment at an Apple Store.

Does this change anything or allow for another solution?

No. I don't have any other suggestions. Good luck.

, I have managed to access Photos using an alternative user account.

Were you able to access the Photos library that you were having trouble with in your primary user account?

How is the external HD formatted? It must be formatted OS X Extended (journaled) with ownership set to be ignored in order for multiple users to share the library without permissions issues:

If you want to download the complete library from iCloud you'll have to follow what the message says. If the iCloud Photos Library has all of your photos then there should not be an issue.

You can always make a backup copy of the current library before deleting the incomplete items and progressing with the download.

I have photo on my hard drive and also iCloud. I assume I need to back them both up? I assumed copying my hard drive using CCC would do but I do not find how to download all contents of my iCloud?

All you need to do is backup the Photos library that you current have on your boot drive. The iCloud Photo Library is a duplicate of your Photos library as long as it's the System Photos library. There's no backing up the iCloud Photo Library. As you make changes to your Photos library the same changes will be made to the iCPL.

The only time you would want to download all of the original files from the iCloud Photo Library is when you plan on disabling the iCloud Photo Library.

If you're using the iCloud Photo Library on all machines then all of the libraries will contain the same photos. Therefore if you backup your Photos library on your iMac it will be backing up all of your photos.