Since FileSieve 4.20, directory and file names that exceed ~240 characters are fully supported. In-order to take advantage of the long names support, the Windows environment that FileSieve runs in will need to have the feature enabled.

To enable the feature, the Windows Group Policy Editor will need to be used, and the relevant setting will need to be enabled.

  1. In the Windows start menu or in the Run dialog (Windows Key+R), type either Edit group policy or gpedit.msc. Press Enter to run it.
  2. In the Local Group Policy tree item on the left, navigate to Local Computer Policy > Computer Configuration > Administrative Templates. In the list on the right, find Enable Win32 long paths.
  3. Double-click on the Enable Win32 long paths item and select Enable at the top-left of the newly-opened window.
  4. Click OK at the bottom of the window.
  5. (Re)Start FileSieve and long names should now be available. If not, try restarting Windows.

Please see this post if more information is required.