Just a little bit more specifiaction.... The componenent was created in a 'single' namespace originaly with 'new component' on the contextual menu on the project. After I chaged the namespace fora nested namespace(now the component desapear from toolbox). if I decide to create a componenent whit the contextual menu on a sub folder in the project, my componnent is in a nested namespace and appear in the toolbox.
I'm working with Visual Studio 2008 - C# - .NET 3.5. after each change I always rebuid and even try to close and reopen the solution (fro try to flush the toolbox caching)
any explication?