Mark, thanks for responding. I've logged onto my computer as that user. Added and updated an event. The Calendar did not revert back to an older month. "Yes", I had the user, on her computer, use Firefox. She added and updated an event. The Calendar did not revert back to an older month.
I've flushed DNS, and Deleted temporary Internet files and History. The user has not added programs or changed programs on her computer. The user won't allow me to delete her profile and create a new one. It's probably something with IE and/or ??