I find the solution

in my case :

i make shore, that in my web part , i not Dispose SpWeb that get from SpContext.Curre.

Example:

SPWeb myWeb =  SPContext.Current.Web;

...

myWeb.Dispose();

This is wrong disposing.

Or othe web or sites, that gets from  Current Context.

Hear is more information about Disposing SPWeb

www.artemiscorp.com/.../disposing-of-spweb.aspx

I ran across this error while trying to insert a webpart into my default.aspx page from Sharepoint designer. The insert webpart action failed and this error was given. My issue was that the webpart's default view was set to Gantt Chart. I set the default view to be basic  list view and managed to insert the webpart succesfully. Afterwards i changed the webparts view to the Gantt Chart view.