Safe Boolean Idiom cannot compile with Visual C++ 10(2010)

[CBasicNet]

Hey guys, I have derived my class from the C++ safe bool idiom class from this page : The Safe Bool Idiom by Bjorn Karlsson

class Element : public safe_bool<>
{
public:
	bool Exists() const;
	bool boolean_test() const { return Exists(); }; // boolean_test() is a safe_bool method
}

When I tried to use it in the if expression like below

Element ele;
...
if(ele)

I got an error like error C2451: conditional expression of type 'Element' is illegal. If I try to cast it to bool, I got this error,

Element ele;
...
if((bool)ele)

error C2440: 'type cast' : cannot convert from 'Element' to 'bool'

This is the 1st time I am using safe bool idiom, I am not sure if this is not allowed or a bug in Visual C++ 10. Any comments?