HELP-Beginner pig lating program

[Icshorts]

I have an error code of.
1>------ Build started: Project: LAB5B, Configuration: Debug Win32 ------
1> main.cpp
1>c:\users\610pawn\documents\visual studio 2010\projects\lab5b\lab5b\main.cpp(31): error C2678: binary '!=' : no operator found which takes a left-hand operand of type 'std::string' (or there is no acceptable conversion)
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\system_error(425): could be 'bool std::operator !=(const std::error_code &,const std::error_condition &)'
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\system_error(432): or 'bool std::operator !=(const std::error_condition &,const std::error_code &)'
1> while trying to match the argument list '(std::string, char)'
1>c:\users\610pawn\documents\visual studio 2010\projects\lab5b\lab5b\main.cpp(31): fatal error C1903: unable to recover from previous error(s); stopping compilation
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========


my code is:
// PigLatin Program
#include <iostream>
#include <iomanip>
#include <string>
#include <cctype>


using namespace std;

string pigLatinString(string, string);
int main()
{
cout << " Welcome to the Pig lating Program!" << endl;
cout << " * You will be prompted to enter a string of * /n" << " *words. The string will be converted into * /n" << " * Pig Latin and the results displayed. * /n" << " * Enter as many as you would like. * /n" << endl;
string originalString = " ";
string newString = " " ;
string word = " " ;
size_t start =0;
size_t begin =0;

while ( originalString != ' ')
{
cout << " Enter a group of words or ENTER to quit: " << endl;

getline(cin,originalString);

pigLatinString(originalString, newString);

cout << pigLatinString(originalString,newString);
}


return 0;
system("pause");
}
string pigLatinString(string originalString, string newString)
{
string word = " " ;
size_t start =0;
size_t begin =0;

while(originalString != ' ' )
{
originalString.find(' ', start);
if( start == string::npos)
return 0;
else
originalString.substr(begin,start - begin) = word;
word.substr(0,1) + "ay" + ' ' = newString;
start ++;
begin = start;

}

word = originalString.find(begin, start - begin);
cout << word << endl;

word.substr(0,1) + "ay" + ' ' = newString;
return newString;




}
I can't figure out why it won't accept the !=