Error: Required skin part area cannot be found.

Problem:

Error: Required skin part area cannot be found.
    at spark.components.supportClasses::SkinnableComponent/findSkinParts()[C:\flexsource\frameworks\projects\flex4\src\spark\components\supportClasses\SkinnableComponent.as:549]
    at spark.components.supportClasses::SkinnableComponent/loadSkin()[C:\flexsource\frameworks\projects\flex4\src\spark\components\supportClasses\SkinnableComponent.as:524]
    at spark.components.supportClasses::SkinnableComponent/validateSkinChange()[C:\flexsource\frameworks\projects\flex4\src\spark\components\supportClasses\SkinnableComponent.as:280]
    at spark.components.supportClasses::SkinnableComponent/createChildren()[C:\flexsource\frameworks\projects\flex4\src\spark\components\supportClasses\SkinnableComponent.as:250]
    at com.riageeks.geek.core::GeekBase/createChildren()[C:\riageeks\geek\trunk\geek\src\com\rg\geek\core\GeekBase.as:71]
    at mx.core::UIComponent/initialize()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:6510]
    at mx.core::UIComponent/http://www.adobe.com/2006/flex/mx/internal::childAdded()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:6402]
    at mx.core::UIComponent/addChildAt()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:6109]
    at spark.components::Group/addItemToDisplayList()[C:\flexsource\frameworks\projects\flex4\src\spark\components\Group.as:1588]
    at spark.components::Group/http://www.adobe.com/2006/flex/mx/internal::elementAdded()[C:\flexsource\frameworks\projects\flex4\src\spark\components\Group.as:1153]
    at spark.components::Group/setMXMLContent()[C:\flexsource\frameworks\projects\flex4\src\spark\components\Group.as:409]
    at spark.components::Group/set mxmlContent()[C:\flexsource\frameworks\projects\flex4\src\spark\components\Group.as:359]
    at spark.components::SkinnableContainer/set mxmlContent()[C:\flexsource\frameworks\projects\flex4\src\spark\components\SkinnableContainer.as:563]
    at spark.components::SkinnableContainer/createDeferredContent()[C:\flexsource\frameworks\projects\flex4\src\spark\components\SkinnableContainer.as:1084]
    at spark.components::SkinnableContainer/createContentIfNeeded()[C:\flexsource\frameworks\projects\flex4\src\spark\components\SkinnableContainer.as:1098]
    at spark.components::SkinnableContainer/createChildren()[C:\flexsource\frameworks\projects\flex4\src\spark\components\SkinnableContainer.as:843]
    at mx.core::UIComponent/initialize()[C:\flexsource\frameworks\projects\framework\src\mx\core\UIComponent.as:6510]
    at spark.components::Application/initialize()[C:\flexsource\frameworks\projects\flex4\src\spark\components\Application.as:708]
    at thingsapp/initialize()
    at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::childAdded()[C:\flexsource\frameworks\projects\framework\src\mx\managers\SystemManager.as:2263]
    at mx.managers::SystemManager/initializeTopLevelWindow()[C:\flexsource\frameworks\projects\framework\src\mx\managers\SystemManager.as:3610]
    at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::docFrameHandler()[C:\flexsource\frameworks\projects\framework\src\mx\managers\SystemManager.as:3395]
    at mx.managers::SystemManager/docFrameListener()[C:\flexsource\frameworks\projects\framework\src\mx\managers\SystemManager.as:3253]

Solution: In Gumbo, you define your skin part with either required=true or required=false. And then that skin need to be defined in your Skin file, which starts with "SparkSkin". If you have defined required=true then it should be defined out of the <Declarations> tag, if you have defined required=false, then it should be defined in <Declarations> tag. In both the cases, variable name and skin id should match (i.e. variable name defined in your source file and id given in Skin file)