Functor compile time error

My code -

#include <iostream>
#include <vector>
#include <string>
#include <sstream>
using namespace std;

#include "boost\numeric\ublas\matrix.hpp"

typedef boost::numeric::ublas::matrix<float> matrix;


class FillMat{  
public:
    FillMat(float valIn) : val(valIn){}
    float operator()(float in) {
        val = in + 1;
        return val;
    }
private:
    float val;
};

typedef boost::numeric::ublas::matrix<float> matrix;
int main(){
    matrix m1(10, 20);
    float init = 22.2;
    FillMat myFiller(init);

    generate(m1.begin2(), m1.begin2() + m1.size1()*m1.size2(), myFiller);


    return 0;
}

When I try to compile the code, I get the following compile time error.

Error   3   error C2064: term does not evaluate to a function taking 0 arguments    

Can someone please tell me why?

P.S. I added the headers. I am using Boost matrix for 2D array.