"You do not have permission" message

I received the following message when trying to access a thread from my email notification:

PriusRos, you do not have permission to access this page. This could be due to one of several reasons:

1. Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
2. If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.

It sounds like I did something wrong but I don't think I did. When I went to the forum and looked for the thread, I could no longer find it. Does this message actually mean that the thread no longer exists (rather than I don't have permission to view it)? Or does it really mean I have been locked out of it?

It usually means that the thread was deleted by a moderator, or possibly combined into another thread. It happens on RSS feeds when the thread is deleted because it is spam or started by a troll.