Due: unknown error (DueTimer? Scheduler?)

Official Hardware Mega Due
1

compiling my Due program I get a unknown error message, not sure what it's related to
(maybe related to one of my included libs DueTimer? Scheduler?)

c:/dokumente und einstellungen/user1/anwendungsdaten/arduino15/packages/arduino/tools/arm-none-eabi-gcc/4.8.3-2014q1/bin/../lib/gcc/arm-none-eabi/4.8.3/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-timesr.o): In function _times_r': timesr.c:(.text._times_r+0x2): warning: undefined reference to _times'

what does that mean?
Is that a known issue?

void setup() {
   // *SNIP*

      i=100;   // 0.1 ms
      Timer3.attachInterrupt(encHandler).start(i);    
      delay(50);
     
 
  //------------------------------------------------------------------------------------
  // attach Scheduler tasks

     Scheduler.startLoop(Task_PollSensors_Slow);

     Scheduler.startLoop(Task_IMU);
     delay(100);                                    // wait for IMU sensor fusion to initialize

       
     Scheduler.startLoop(Task_Navigator);

   // *SNIP*