Google does not allow you to use adsense on pages that are for registering or logging in or anything like that. Your best way to do is to add this code to your website:
Code:
<if condition="THIS_SCRIPT != 'login' AND THIS_SCRIPT != 'private' AND THIS_SCRIPT != 'register' AND THIS_SCRIPT != 'usercp' AND THIS_SCRIPT != 'faq'">
YOUR ADSENSE CODE
</if>
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