Hi - Is there any reason why someone would find that he cannot post in a particular thread? In my case, I would like to add a comment to the thread: What exactly is a "Positional Player"? but am unable to do so. Thanks.

Probably the person that started the thread (yeres30) has blocked you.

Blocked because of my comments? How odd! Oh well, it's an interesting thread anyway and I'm certainly not going to lose any sleep over it.

Not necessarily due to comments. The block is non discriminatory it hates everything.

http://support.chess.com/Knowledgebase/Article/View/38/0/how-can-i-block-another-user

Once blocked, a member cannot do any of the following:

• post notes to your account 
• send you messages, 
• accept your game seeks
• be auto-matched with you in open seeks 
• join tournaments that you are running 
• post in content that you created

Hmm, I wonder what I have done to deserve that! *shrug* But life's too short to worry about trivia.

Don't worry about it. Some people are extra-cranky.