Error -205177: Reference Error - Undefined Variable.

Hello Experts,

I am working on TruClientIE protocol version 12.02. Am capturing visible text from the application screen using "Evaludate JS on Object" funtion. 
Steps to Capture Visible Text

1. Drag out “Evaluate JS on Object” from the Toolbox
2. Click on “ Click on Choose an object” and highlight the object wanted
3. In the “Step” drop down tab of the step, change the Action from “Evaluate JavaScript” to “Get Property
4. In the “Argument” section of the step, In the property box select “Visible Text” and in the Variable box type: “VisibleText”

Now to validate above, I am using  “Evaluate JavaScript”, with code window.alert(VisibleText);

But getting below error message on above validation steps 

Evaluate JavaScript Code window.alert"VisibleText"; failed - exception occured: ReferenceError "VisibleText" undefined 

Why “VisibleText” is undefined? How and where to define it ?

Thanks