Did you run the Clean... Command from the Project menu in Flash Builder?
Error: E0011E: Invalid feature layer: at com.esri.ags.layers::FeatureLayer/initLayer()at Function/com.esri.ags.layers:FeatureLayer/private:loadDetails/com.esri.ags.layers:myResultFunction() at mx.rpc::AsyncResponder/result() at com.esri.ags.tasks::DetailsTask/handleDetails() at Function/http://adobe.com/AS3/2006/builtin::call() at com.esri.ags.tasks::BaseTask/handleResultEvent() at mx.rpc::AsyncResponder/result() at mx.rpc::AsyncToken/http://www.adobe.com/2006/flex/mx/internal::applyResult() at mx.rpc.events::ResultEvent/http://www.adobe.com/2006/flex/mx/internal::callTokenResponders() at HTTPOperation/http://www.adobe.com/2006/flex/mx/internal::dispatchRpcEvent() at mx.rpc::AbstractInvoker/http://www.adobe.com/2006/flex/mx/internal::resultHandler() at mx.rpc::Responder/result() at mx.rpc::AsyncRequest/acknowledge() at DirectHTTPMessageResponder/completeHandler() at flash.events::EventDispatcher/dispatchEventFunction() at flash.events::EventDispatcher/dispatchEvent() at flash.net::URLLoader/onComplete()
Adobe Flex SDK versions
The minmum supported software development kit (SDK) version is Adobe Flex SDK 4.6. For detailed Flex framework system requirements, read the current Flex SDK system requirements by Adobe.
How are you using FeatureLayer in your code?
Are you using the Adobe 4.6 SDK?