[WP3.0]Theme Editor – Edit header.php

Hi There, I’m using WP3.0 and with default twenty ten themes, i try to edit my header.php file and do an update. it shows me the error below:

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Method Not Implemented

POST to /wp-admin/theme-editor.php not supported.
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I’ve done some research and somebody say it’s due to host configuration or .htaccess. But i actually can’t find any solution on this problem. Do the experts have any idea on this problem? If it’s setting on .htacess may i know what will be the key settign for this problem?