Unable to add files/folders to Quick Access on Windows 10: "Unspecified Error"

To fix this issue go to these two folders:

• %AppData%\Microsoft\Windows\Recent\AutomaticDestinations
• %AppData%\Microsoft\Windows\Recent\CustomDestinations

Then delete all the files in those folders. This should fix the issue without any further action.

Source: SinsOfRube on Reddit

Turning off the automated features of quick access fixed my problem:

In Windows Explorer, on the tool-ribbon, in the View tab, under options, select "Change Folder and Search Options," In the Folder Options dialog, in the Privacy section at the bottom:

• uncheck "Show recently used files in Quick access"
• uncheck "Show frequently used folders in Quick access"

Once I did this, I was able to drag a folder to Quick Access which had only give me the red "forbidden" circle before.

P.S. Even with all the "show" options in the Folder Options View tab turned on and all the "hide" options turned off, I still do not see %appdata%\microsoft\windows\Recent\AutomaticDestinations\ in Windows explorer unless I paste the full path in the explorer address bar. Instead, I see %appdata%\microsoft\windows\Recent Items, which appears to be a "virtual" (fake) file.