🚀 go-pugleaf

I can't figure out why this code doesn't work.  I searched through the
include files for map and xtree but couldn't figure out what they were
doing.
I am basically assigning a new value to all my entries in a map via an
iterator:

--cut--

typedef std::map<int, MyClass*, std::less<long> > MyContainer;
typedef MyContainer::iterator MyIterator;

MyContainer myContainer;

void OrderSequentially()
{
    int key = 0;
    MyIterator iter = myContainer.begin();

    while(myContainer.end() != iter)
    {
         (*iter).first = key++;
         iter++;
    }
}

--cut--

The compiler (VC6 sp3) complains with "error C2166: l-value specifies const
object" and points to the line:

(*iter).first = key++;

Why is this? I am not using a const iterator.

Thanks