I am trying to run Add-AzureRmAccount cmd by passing id and pwd using System.Management.Automation.PSCredential. But I am getting an error "Sequence Contains no elements" error. As a workaround I have added AAD account(firstname.lastname@example.org) and it is still not working.
That's not an awful lot of detail, unfortunately. Are you saying you're trying to hardcode a password, rather than type it in? Can you share any of the commands you're attempting to run? Without seeing what you're typing, it's pretty hard to guess what might be wrong.