How to call NewWorkItem (COM) in C

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I am trying to use NewWorkItem to scheduler a task in MS scheduler for windows 2000/XP.

The below code works for C++ but I get an error saying:
"NewWorkItem' : is not a member of 'ITaskScheduler'" when I try to use it in C.

hres = pITS->NewWorkItem(&pwszTaskName, // Name of task
&CLSID_CTask, // Class identifier
&IID_ITask, // Interface identifier
(IUnknown**)&pITask); // Address of task interface


I am a C++ programmer and new to the ways of C-world. Please help.