Dear Anu,
I got the same error to download the SAP Note 1680583 from SAP Marketplace.
In my case, the identified solution was to download the SAP Note directly from Download Basket.
1) Include the note into SAP Download Manager (Click on download button)
2) Click on Go to Download Basket or Maintain Download Basket
3) Click on link of SAP Note (Description column)
4) A ZIP file will be downloaded into your computer
5) Unzip the SAP-NOTE.ZIP file
6) Call SNOTE and upload the resulting SAP-NOTE.txt file
7) Proceed witn SNOTE next steps
Regards,
Herman Arancibia