how to define a member function of template class which return a nested class object

template<typename IPC_TYPE>
Poller<IPC_TYPE>::Event Poller<IPC_TYPE>::wait(size_t max_wait_time = 50)
{
    Event e;
    return Event();
}

I define a class template Poller and also a nested class Event, I am writing a member function of Poller which return a Event object,but the compiler reports " Error C2061 syntax error: identifier 'Event' IPC poller.cpp 8 ", how should I do? thank you!