How can't I?

[Maxb2020]

How can't I post comments on some threads?

[Erasmus]

It depends. What are some of the threads that you can't you can't reply to?

[nice]

How can't I post comments on some threads?

They may be locked

[Cognizant]

If the thread is locked, nobody but moderators/administrators can post in that thread.
Threads get locked for multiple reasons, but usually the most recent post/last post is the one that states the reason.

[DerBear]

Everything in the puberty 101 Archive is locked and in other forums, the last post will tell you why a thread was locked.

Sometimes you might have entered a thread just before it was about to be locked and you made a post when it was in the process of being locked, that would bring up an error message.

However you'll always know why a thread was locked due to the bottom/last post in the thread.