problem with linklist

template<class T>
void TimerDLList<T>::addFirst(TimerItem<T>* const itemPtr)
{
// suppose itemPtr is not pointing to NULL

itemPtr->prev = (TimerItem<T>*) NULL;

head = (TimerItem<T>*)NULL;

if (tail == (TimerItem<T>*)NULL ) // nothing in the link list
{
tail = itemPtr;
itemPtr->next = (TimerItem<T>*) NULL;
}
else
{
itemPtr->next = head;
head->prev = itemPtr;
}

head = itemPtr;
}



there seems to be some problem in head->prev = itemPtr.
There seems to be some corrution at this point.
PLEASE HELP.......
seems like head->prev is accessing a wrong address.

.