Does the Catalog show the Preview with the 'missing' icon [ ! ] ? NO Does it exist? Can you locate it in Windows File Explorer? YES Can you Right-click the photo in the Lr library grid and choose [Show in Explorer] ? YES When found, can you check the Properties/Attributes of the photo file and its containing folder? (It cannot be checked as Read-Only or Hidden) EXCEPT FOR USER EVERYONE, THE PERMISSIONS ARE FULL INCLUDING WRITE. You might also check the "Additional External Editor" presets in the Preferences dialog to see if the ON1 Preset has the wrong location for the ON1 software .exe file. Or re-install the "plug-in". REINSTALLED PLUGIN WITH SAME RESULTS. ALSO, UNDER LIGHTROOM'S PLUGIN MANAGER, ALL ON1 PLUGIN MODULES ARE SHOWN AS INSTALLED AND RUNNING WITH A GREEN LIGHT. ON1 PLUGIN WORKING FINE IN PHOTOSHOP. Your other question also sounds like a Read/Write permissions problem, if you cannot save photos to the drive specified as the Destination
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