Try with the following code/method.
Code:
Obj="provide required screen/object name"
iValue="provide required checkbox value to check"
If obj.getroproperty("enabled") AND obj.Exist Then
If UCase(iValue) = "ON" OR UCase(iValue) = "TRUE" OR UCase(iValue) = "SET" OR UCase(iValue) = "SELECT" Then
iValue = "ON"
MySet = obj.set(iValue)
End If
If UCase(iValue) = "OFF" OR UCase(iValue) = "FALSE" OR UCase(iValue) = "UNSELECT" OR UCase(iValue) = "" Then
iValue = "OFF"
MySet = obj.set(iValue)
End If
End If