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In order for the download function in the web interface for the Nokia store to work you need to login using your Nokia Account. At the top-right of the page you should see a link from which you can sign in. Also make sure you have selected your phone model to see only apps suitable for your device.
Hope this helps,
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of course I've logged in and I've selected my phone model, but still doesn't working.when I press the button for downloading on pc, a message appears: "Error occurs". and this is available for all apps in ovi suite.