I've search high and low for a solution to this error.
I had given up after over a year of trying to resolve it, on Windows 10. I've pickup up a new PC on Windows 11 and tried to install the latest version from the Windows Store and low and behold, this issue has come up again!
I've been through every single community post here, and in the Apple Communities. I'm happy to report that I've uncovered the cause, but can't find a solution.
When I install iCloud for Windows on a clean Windows 11 machine, the app places iCloud Photos and iCloud drive at;
and if you have Microsoft OneDrive, it gives a message that says something to the effect that OneDrive is the users home directory, so the iCloud folder is actually placed in the user's root folder;
...but when I install on a machine that has DROPBOX, AND has the user's Pictures folder inside DropBox, the folders are placed at;
BAM, the error occurs!
However, if DropBox is not installed, no problem. And if, Dropbox is installed and the user's Pictures folder is not inside Dropbox, no problem. As soon as the user has their Pictures folder inside Dropbox, then no love and the error results.
So iCloud for Windows is testing for the presence of a user's home folder being inside Microsoft One Drive and correctly handling that use case, but it does not do the same test for Dropbox and also correctly handle that use case.
It may even be that a user's home folder inside any cloud solution is a problem, but since this app is downloaded through the Microsoft store, they tested it for OneDrive and made it work only with that solution! That's messed up!
Anyone have ideas on how to solve this issue? I'd like to also have DropBox engineering work with Apple and Microsoft to perform the same kind of installation handling that the app does when it finds OneDrive! The solution is to simply have iCloud for Windows test for Dropbox and if Pictures is found inside DropBox, handle it the same way it does with OneDrive, just place the iCloud Photos folder in the User's profile root folder!