That's the result of an old bug. Basically, if you tried to login as "DyLaN", the system would still log you in. The error occured when the system would associate any new posts made with the username "DyLaN", which doesn't match your actual username "dylan" and as such it doesn't think you made the post.
This has happened to me as well.
I think Ross has it so you can't edit week old post.
If you don't know, don't answer. Guessing just causes confusion.