To download a SQL file from an IIS hosted website the website needs to know how to handle the file.
In general terms a SQL file is plain text, so the respective MIME type would be text/plain
This can be added to IIS manually using the MIME types editor. Or for a more reliable approach add the MIME type to your application web.config file – this will make the settings portable so they get deployed with the application (and will work on any instance of IIS), for example;
<configuration> <system.webServer> <staticContent> <mimeMap fileExtension=".sql" mimeType="text/plain" /> </staticContent> </system.webServer> </configuration>