ArgumentError: Undefined state 'up'.

Problem:

ArgumentError: Undefined state 'up'.
    at mx.core::UIComponent/getState()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:9030]
    at mx.core::UIComponent/findCommonBaseState()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:9050]
    at mx.core::UIComponent/commitCurrentState()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:8881]
    at mx.core::UIComponent/creationCompleteHandler()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:10429]
    at flash.events::EventDispatcher/dispatchEventFunction()
    at flash.events::EventDispatcher/dispatchEvent()
    at mx.core::UIComponent/dispatchEvent()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:11262]
    at mx.core::UIComponent/set initialized()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:1513]
    at mx.managers::LayoutManager/doPhasedInstantiation()[C:\flexsource\frameworks\projects\framework\src\mx\managers\LayoutManager.as:757]

Solution: You have defined a skin for a component and that skin expects some states to be defined for the component. e.g. a Button expects 4 states to be defined in Skin. Below is a basic skin for a Button.

<?xml version="1.0" encoding="utf-8"?>
<s:SparkSkin xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo" >

    <s:states>
        <s:State name="up"/>
        <s:State name="over"/>
        <s:State name="down"/>
        <s:State name="disabled"/>
    </s:states>
    <s:Rect height="100%" width="100%">
        <s:fill>
            <s:SolidColor color="#0000FF"/>
        </s:fill>
    </s:Rect>
    
</s:SparkSkin>