Error in Scheduler : Func $res = call_user_func($func,);

[Elizabeth2010]

Hi. I have Problems with Sugar Scheduler.
I recived this error : Warning: call_user_func(updateTrackerSessions) [function.call-user-func]: First argument is expected to be a valid callback in D:\...modules\Schedulers\Scheduler.php on line 140

System features:
SugarCrm Comunity Edition
MySql 5.1
Windows 2003 server
Php 5