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If you get an error message that the Nero update failed to download in Nero Start, there might be some network issue.
Generally, you can just delete the temporary files for updates and retry the download again to solve the update download issue.
Here is the brief instruction to delete the temporary files in Nero Start:
Click on the icon in the upper right corner of Nero Start, select "Options" .
Go to the "Temporary files" paths, click the "Delete" button, and then go back to the "Updates" page to download and install the application again.