The instructions for the tinymce "plugin" says to change the definition of tep_draw_textarea (- In admin/includes/functions/html_output.php) to be:
function tep_draw_textarea_field($name, $wrap, $width, $height, $class, $text = '', $parameters = '', $reinsert_value = true) {
the new parameter (class) should be at the end:
function tep_draw_textarea_field($name, $wrap, $width, $height, $text = '', $parameters = '', $reinsert_value = true, $class='') {
and the call to tep_draw_textarea_field should instead be:
<?php echo tep_draw_textarea_field('products_description[' . $languages[$i]['id'] . ']', 'soft', '70', '15', (isset($products_description[$languages[$i]['id']] ) ? $products_description[$languages[$i]['id']] : tep_get_products_description($pInfo->products_id, $languages[$i]['id'])), 'mceEditor'); ?>
The reason being is that there are alot of calls to tep_draw_textarea_field using 5 or more parameters, and by adding teh new parameters in the middle, the original fifth becomes the sixth and the sixth becomes the seventh, and teh calls become really screwed up.
This change to the instructions will fix the mail.php error as well.