This is lifted straight from the weekly geocaching newsletter. And worth reiterating here...

When a geocacher posts a “Needs Maintenance” log to your cache page, the page displays a Needs Maintenance attribute (a colored cross).  To let other geocachers know that you have fixed the maintenance issue, you need to remove the Needs Maintenance attribute by posting an “Owner Maintenance” log. You must take this step even when posting an “Enable” log, as this does not automatically remove the attribute.

From the Knowledgebase – Caches that Need Maintenance