Windows List appears not to work with TLB 6.5.1 (64 bit) beta. Instead of displaying a list of the 12 open windows, it lists only one of the windows.
Windows List plugin does not depends of TLB version. Please check if the windows are listed in the standard windows task switcher (press ALT+Tab and hold down Alt key).
Also maybe some windows are hidden in the menu. Right click in the Windows List menu and check is there the "Show Hidden" menu item.