I think the value that you assign to CheckBoxList is not in array, for example some where you will define:

"IsMVP"=>"Y"

It should be in array "isMVP"=>array("Y")

It seems to me that you want only single checkbox for "Y" or "N" so just add only 1 option for CheckBoxList:

<?php
CheckBoxList::create(array(
    "name"=>"IsMVP",
    "data"=>array(
        "Yes"=>"Y",
    )
));
?>

You do this:

In the report controller:

class MyReport
{
    use \koolreport\inputs\Bindable;
    use \koolreport\inputs\POSTBinding;
    protected function defaultParamValues()
    {
        return array(
            "IsMVP"=>array('Y'),
        );
    }

    protected function bindParamsToInputs()
    {
        return array(
            "IsMVP"
        );
    }    
    ...

}

And in the view:

<?php
CheckBoxList::create(array(
    "name"=>"IsMVP",
    "data"=>array(
        "Yes"=>"Y",
    )
));
?>

Hi, one thing I want to ask: Normally we use list of CheckBox when we have multiple options to choose. And for the "Yes" and "No", we should use RadioBox or single CheckBox. Why do you want to use CheckBoxList for "Yes" and "No" option because user can choose both yes and no?

Understand. So you do exactly like my above code (including the report controller class). You notice that I set the "IsMVP"=>array('Y') in the defaultParamValues() function. This will make the CheckBoxList select "Yes" as default. If you do not want to select "Yes" as default, you set "IsMVP"=>array() (empty array).

So you may wonder how do we know which option user selected. So basically, after user post the form, you can get value from $this->params["IsMVP"] as array. If user select "Yes", you will receive value array('Y'), if use don't select then you will get array(). You can check "Yes" or "No" simply with isset($this->params["IsMVP"][0])

Let me know if you need further explanation.