Boolean expected 

You attempted to invoke the Boolean.prototype.toString or Boolean.prototype.valueOf method on an object of a type other than Boolean. The object of this type of invocation must be of type Boolean. For example:

var o = new Object;

o.f = Boolean.prototype.toString;

o.f();

To correct this error

• Only invoke the Boolean**.prototype.toString** or Boolean.prototype.valueOf methods on objects of type Boolean.

See Also

Reference

Boolean Object (JScript 5.6)

Concepts

Data Types (JScript 5.6)
Controlling Program Flow
Copying, Passing, and Comparing Data (JScript 5.6)