Error 1 & 2
Error Message : Internal Server Error - Something is broken. Please post to the group so the Twitter team can investigate.
This message informs you that Twitter is currently experiencing issues and made you request failed.
Error Message : Forbidden - The request is understood, but it has been refused or access is not allowed. An accompanying error message will explain why. This code is used when requests are being denied due to update limits.
Usually when I see this message it is often related with credentials. Please verify your credentials and the application contains all the required authorizations.
Few days ago Twitter reset some of the user credentials so please verify this.
You also need to verify your rate limits. If you are attempting to perform the same request for multiple users you might find yourself facing rate limit issues.
You can get your rate limits with this code:
var rateLimits = RateLimit.GetCurrentCredentialsRateLimits();
I cannot really explain this one. I have verified and there is no user with this id so I do not understand why you received this Id in your Followers, maybe the account has been removed, I honestly don't know.
As these issues are not "common" I will be happy to give you more information if you provide me your code.
Please keep me up to date.