Is this still an open issue? I am getting the same error exactly the original thread mentioned. Sounds like the URL that quicken has you redirect to with Citi does not work. I even tried the same URL trying to retrieve my Citi Home Depot user ID to see if it will find it and "encountered and error". SO, that URL is not working. Not sure if its on the Citi side or they should have Quicken redirect to and updated URL for the authorization of the account.
I goto a completely different URL to login to my Citi Home Depot account and this has worked fine and still lets me login to my account with no issue.
The thread stated that the issue is now resolved, but I don't think it is. I have tried different browsers as well per the thread and same results