Hi again, here is small bug (imho)

void ThrowValueTypeError(const String& text, const Value& src, int target)
{
	ValueTypeError err;
	(String&)err = text;
	err.src = text;               // <-- bug, should be err.src= src;
	err.target = target;
	throw err;
}

I would suggest removing this function, instead code following:

class ValueTypeError : public Exc {
public:
	ValueTypeError(const String& text, const Value& src, int target) : Exc(text), src(src), target(target) {}
	Value src;
	int   target;
};

to throw then code

	throw ValueTypeError(String().Cat() << "Invalid value conversion: "
	                    << GetName() << " -> " << typeid(T).name(),
	                    *this, t);

Also no need to return something after the throw to silence the compiler

THX, Hans