An Error Was Encountered While Opening A Window This error often appears when the Lotus Notes client crashes. A reboot generally fixes the problem, but Lotus Notes cannot be restarted if all Notes processes are not terminated properly. Goto task manager and end the Lotus Notes application and then goto processes tab and highlite ntaskldr.exe and end the process and then reopen Lotus Notes or Use KillDomino to kill all the processes that Lotus Notes has left running.