error C2593: 'operator =' is ambiguous; Compiled fine on VS6, but I get that error on VS10

I get the following error:

1>c:\documents and settings\krzys\desktop\desktop icons\ollydbg\plugins\odbgscript\OllyLangCommands.cpp(3602): error C2593: 'operator =' is ambiguous
1>          c:\documents and settings\krzys\desktop\desktop icons\ollydbg\plugins\odbgscript\var.h(45): could be 'var &var::operator =(const long double &)'
1>          c:\documents and settings\krzys\desktop\desktop icons\ollydbg\plugins\odbgscript\var.h(42): or       'var &var::operator =(const int &)'
1>          c:\documents and settings\krzys\desktop\desktop icons\ollydbg\plugins\odbgscript\var.h(41): or       'var &var::operator =(const ulong &)'
1>          while trying to match the argument list '(var, std::streamsize)'开发者_StackOverflow

At this code:

map<string, var> variables;
streamsize sum = 0;

if (sum) {
    variables["$RESULT"] = sum;  // Error 1
    return true;
}

and

class var
{
public:
 ulong dw;
 string str;
 long double flt;
 vtype vt;
 bool isbuf;
 int size;

 var();
 var(const var& rhs); 
 var(string& rhs); 
 var(ulong rhs); 
 var(int rhs); 
 var(long double rhs); 

 // less than zero this < rhs
 // zero this == rhs 
 // greater than zero this > rhs 
 int compare(const var& rhs) const; 
 int compare(const string& rhs) const; 
 int compare(const ulong& rhs) const; 
 int compare(const int& rhs) const; 
 int compare(const long double& rhs) const; 

 string strclean(void);
 string strbuffhex(void);
 string strbuff(void);

 var& operator=(const var& rhs);
 var& operator=(const string& rhs);
 var& operator=(const ulong& rhs); // Error 4
 var& operator=(const int& rhs); // Error 3
 var& operator=(unsigned short& rhs);
 var& operator=(unsigned char& rhs);
 var& operator=(const long double& rhs); // Error 2

 var& operator+=(const var& rhs);
 var& operator+=(const string& rhs);
 var& operator+=(const ulong& rhs);
 var& operator+=(const int& rhs);
 var& operator+=(const long double& rhs);

 void resize(ulong newsize);

};

Compiled perfectly with VS6, but now I'm getting this error with VS10.

Check sum's type and variables's methods. There's a chance they've added new operator= overloads in the switch from VS6 to VS2010.

Your variables map holds values of type var. sum isn't a var, so a conversion needs to be made.

The streamsize type in VC6 is a simple int and the var class will convert that to a var type implicitly.

In VS10, streamsize is an __int64, which you have no implicit conversion to a var for.