This may be occurred when you open the window of Denbun in a separated frame page.
(for example, you use Denbun in the tab menu of desknet's)
If you want to use desknet's tab menu to access to Denbun, desknet's and Denbun are installed on the same server.
If you install Denbun in another server, please use the "Option Menu" or "Bookmarks" in stead of the tab menu.