Getting Error upon generating certificate signing request file in Keychain Access on Mac mini

While generating certificate signing request file in Keychain Access, i am getting an error 'Unknown Error: -2,147,409,850'. Tried many solution but nothing worked for me. Please help

1. Steps to reproduce the error.     
   1. Open Keychain Access application in mac system
   2. Click in app title (Keychain Access) on top left corner near to apple icon
   3. Form the dropdown options select -> Certificate Assistant -> Request a Certificate from Certificate Authority
   4. In the Certificate Information window, give email address and select “Saved to disk” option -> Continue.
   5. Select folder to save file -> Save -> Error window comes.

[Edited by Moderator]