std::map problem

I'm using a data structure of the type:
std::map<std::set<int>,std::set<char*>>, where as you notice that the key is
a set of ints and the value corresponding to it is a set of strings. However,
when I try to map a key to a set of strings such that the set contains more
than 20 strings, the mapped value is empty. For example if I do something
like this:

----------------------------------------------
std::map<std::set<int>,std::set<char*>> mapInt2Char;
std::set<int> setKey;
std::set<char*> setValues;
char *pChar = null;

setKey.insert(1);
for(i - 0;i < 25;i++)
{
  pChar = new char[10];
  sprintf(pChar,10,"%d",i);
  setValues.insert(pChar);
}

mapInt2Char[setKey] = setValues;
-----------------------------
I find that the value corresponding to the key {1} in the map is empty. It
works fine as long as the number of strings in the set is less than or equal
to 20. I don't get this problem when the mapped value is a set of ints. Does
anybody know why this is happening? I'm using VS 2005.