Workflow transition date check is incorrect

In workflow.module, you do:

      if ($node->workflow_scheduled_date['month'] < 10) {
        $node->workflow_scheduled_date['month'] = '0' .
        $node->workflow_scheduled_date['month'];
      }

This is totally incorrect, if the month is already "01", then the if will return true and the result will be "001". Then the strtotime() fails.

You should use sprintf to reformat the date. Attaching a simple patch.