While not necessary to use, you have the option to utilize a locally installed version of Photoshop to optimize images for the device you are designing for. This article offers some tips on dealing with an error when using this option.
For more information on the downscaling option, read the article Using Photoshop to Downscale Images.
If you receive this error while exporting your Vertical, there are several items which may be at fault:
- Make sure you have selected the correct version of Photoshop that is installed on your local machine in the "Photoshop Version" drop-down menu.
- Make sure Photoshop is already running when exporting a Vertical.
- If you have multiple versions of Photoshop installed, the mag+ InDesign plugin may not be able to adequately find the application. Try uninstalling older versions of Photoshop so that only a single application remains on your machine.
- On occasion, the type of resampling method you choose might throw errors. Try a different method of resampling.