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In Drive, there is functionality known as Expanded Folder Permissions, which allows a user to share different levels of a folder tree with different people and at different permission levels.
When using this functionality, if the top level folder is going to be shared then you’ll want to share that first, before sharing any of the subfolders beneath.
If you share a subfolder first and then try to share the top level folder above it later, you will be blocked from doing so due to the fact there is already a shared folder beneath it.
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