Some Windows applications apparently require "Rundll32.exe" application to run in the background. The Windows Rundll32 Program is used to run DLLs as programs and is used by many programs to execute functions located in a DLL file. By terminating this process using Windows Task Manager, the problem with the calendar is solved; however, some other program may be affected.
Downloading XP Service Pack 1 eliminated that background program, Rundll32.exe, on my PC with the calendar problem.
My advice for those with the problem:
1) Confirm Rundll32.exe is running in background;
2) Download Windows XP Service Pack 1 and see whether Rundll32.exe is still running;
3) If so, "end process" with Windows Task Manager and then test for effects on any other problems.