yahoo messenger invalid ID on BB curve 9300

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I bought a new Blackberry Curve 9300 last week. I choose this mobile phone because of the features Instant messaging. But I have a problem logging in my yahoo id it always say's invalid yahoo id or password. I've checked the BB forums already and they says this something about using some special character. But I only use alphanumeric characters. In MSN it is working fine. Another problem is my keypad light. I want to make it brighter but their is no opstion to make it brighter. Can any one help me regarding this problem of my BB Curve 9300? I really appreciate if you could give me some instruction for this.