[ns] compiling error

[Liu Gengpu]

Hello all ns users:
When I was compiling my new agent,I met such error listed below.
I dirived the class TryTimer from TimerHandler.

"try.h"
............
class TryTimer : public TimerHandler {
public:
	TryTimer (TryAgent *a): TimerHandler() { a_ = a;}
	void expire(Event *e);
protected:
	TryAgent *a_;
};
......................

"try.cc"
TryAgent::TryAgent() :Agent(PT_PING)
{       //the 12 line!!! error was reported in this line
	bind_time("interval_", &interval_);
}

Here is the error the compiler reported.
......................
try.cc
try/try.cc(12) : error C2512: 'TryTimer' : 
no appropriate default constructor available
............................

By the way,the compiler I used is the nmake of VC6.0.
Can anyone tell me why I got this error? 
Thanks a lot
                       gpliu from ustc of china

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