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- Go to folder %programdata%\Microsoft\Microsoft Dynamics NAV\100\Server\Keys (where 110 is the version of your NAV server, which can be vary)
- Delete the server_name.key file of your server instance
- Go to Dynamics NAV 2017 Administrator > Your Server Instance > Database Credentials
- Enter your database authentication again, the encryption key should be generation again
- Try to start server again
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