iPhoto will not let me move photos in an album manually, despite my checking the manually option in View. Anybody know why? OS X 10.11.6 iMac
iMac (27-inch, Late 2012), OS X El Capitan (10.11.1)
What kind of album? A standard album or a smart album?
For a standard album you should be able to arrange the photos manually.
Is it only one specific album that cannot be rearranged manually, or all albums?
Have you tested, if the problem occurs only in your current iPhoto library, or does it happen in any library? You can test this by creating a small iPhoto Library for testing. (use the command "File > Switch to Library" in iPhoto and select "Create New" in the library chooser panel).
I did all of your suggested tests. All albums (standard) will not let me rearrange photos, nor in the new library I created.
If the problem happens for all libraries, it may be a problem that only happens in your user account, and then deleting the Photos preferences might help, or the problem is system wide. Have you already tried to restart the Mac?
If it is system wide, reinstalling iPhoto might help. To find out, if it is system wide, try to launch iPhoto from the Guest User account. https://support.apple.com/en-us/HT204443
iPhoto will not let me rearrange photos in an album manually.
