C++ :: For Each And Member Function

I can't get this code to compile (using VS2010 and gcc4.6.1):

Code:
#include <string>
#include <vector>
#include <algorithm>
#include <boost/bind.hpp>
class X {
public:
void foo( const std::vector<std::string>& v ){

[Code] ....

VS2010 presents an error message like "member function already defined or declared" and gcc something like "... function can not be overloaded" (very cryptic error message).

If I change the vector to foo to std::vector<int> and let bar() take an int, it works perfectly fine. And if I use boost

Code:
std::for_each( v.begin(), v.end(), boost::bind( std::mem_fun(&X::bar), this, _1 ) );

The above code compiles as well.

While it is perfectly fine for me to use boost I would nevertheless like to understand what's happening here.