This error occurs when the External Editing settings for the plug-ins are set to save the images as PSD files instead of TIFF files. To resolve the issue, please do the following:
- While Lightroom is still open, click Edit> Preferences OR Lightroom > Preferences.
- Click on the "External Editing" tab at the top of Preferences.
- Midway down you will see the Preset drop-down bar. Select the affected plug-in from this list.
- Change the file format from “PSD” to "TIFF.” Set the Bit Depth to 16-bit, Resolution to 240, and Compress to None.
- Click on the Preset bar again and select "Update Preset ..." from the list to save the settings.
- Repeat these steps for each Nik Collection plug-in listed as they should all be set to “TIFF.”
If you receive the same error again after making this change, be sure to select “Edit a Copy with Lightroom Adjustments” instead of “Edit Original” when opening the image.