In the prosilver style, the posting_pm_header.html template has a </ul> closing tag missing from line 76.

[code]
                    <dd class="recipients">
                    <ul class="recipients">
                        <!-- BEGIN to_recipient -->
                        <li>
                            <!-- IF to_recipient.IS_GROUP -><a href="{to_recipient.U_VIEW}"><strong>{to_recipient.NAME}</strong></a><!- ELSE ->{to_recipient.NAME_FULL}<!- ENDIF --> 
                            <!-- IF not S_EDIT_POST -><input type="submit" name="remove_{to_recipient.TYPE}[{to_recipient.UG_ID}]" value="x" class="button2" /><!- ENDIF -->
                        </li>
                        <!-- END to_recipient -->
                    </dd>
[/code]