My chat cannot be readed

If I play on a server and send messages, other players cannot receive my messages. I saw on my friends Computer that he doesn't get my messages. I already checked the Xbox Live Settings with my father, but they say i can chat with all players. My sister has the same Settings and can chat with other Players. I think that this is a bug. It's about my Account with the Gamertag "Luke Hiwalker4". In the pictures below, you can see the chat of my account where i cant send messages [Luke.png] and the chat of my 2nd Account where I can send messages [Assembly.png].