After analyzing what I found is, download code of Magento gives 404 not found code for the downloadable product with space in filename. After removing the space from filename and updating via above SQLs fixed my issue.

After analyzing what I found is, download code of Magento gives 404 not found code for the downloadable product with space in filename. After removing the space from filename and updating via above SQLs fixed my issue:

UPDATE downloadable_link SET link_url = 'http://my-store.com/media/downloadable/files/links/m/y/mysoftware-v202.zip';
UPDATE downloadable_link_purchased_item SET link_url = 'http://my-store.com/media/downloadable/files/links/m/y/mysoftware-v202.zip';