TF30063: You are not authorized ... programmatic access not working

Question

The code below provided in this answer did work well for a while but now its throwing Microsoft.TeamFoundation.TeamFoundationServerUnauthorizedException: 'TF30063: You are not authorized to access https://{mysite}.visualstudio.com/.' again.

var credentials = new VssClientCredentials();
credentials.PromptType = CredentialPromptType.PromptIfNeeded;

var teamProjects = new TfsTeamProjectCollection(tfsCollectionUri, credentials);
teamProjects.EnsureAuthenticated();         // exception thrown

Q How can I fix this problem?

Update Strange enough,

1. before executing teamProjects.EnsureAuthenticated(); the debugger reads PromptIfNeeded for credentials.PromptType.
2. after the exception has been thrown and the debugger has stopped the execution, it reads DoNotPrompt for credentials.PromptType.

Observation The above code works perfectly well in a console application but fails to work in a windows forms application (i.e. it throws an exception).

Q1 How can I make the above code work in a windows forms application?

Answer 1

If you execute the code above within a Task (i.e. a separate thread) it just works. If the credentials are not present or stale at the location in the registry (see this answer) a window opens and you can authenticate yourself.

Can anyone explain why this works?