PROCESS-WAIT error

Hello,

When running the following code I get the error "PROCESS-WAIT called 
when scheduling not allowed":

(in-package :cl-user)

(defparameter *timer* ())

(capi:define-interface status-window ()
   ()
   (:panes
    (text1 capi:text-input-pane  :reader text1))
   (:default-initargs
    :window-styles '( :borderless :hides-on-deactivate
                     :always-on-top :movable-by-window-background)
    :best-x 0 :best-y 0 :width 220))


(defun start-timer ()
     (unless *timer* (setf *timer* (mp:make-timer 'update-message )))
     (mp:schedule-timer-relative-milliseconds *timer* 300 500))

(defun update-message ()
   (let ((message (format () "~a" (get-universal-time)))
         (screen (capi::find-interface 'status-window)))
       (capi:apply-in-pane-process screen
                                   #'(lambda(interface) (setf 
(capi:text-input-pane-text (text1 interface)) message)) screen)))


(start-timer) ;;-> ERROR

Mikael