defender beta2 update

getting the following message when I try to install windows defender beta 2,
also getting the same message when I go to the control panel and try to
uninstall windows defender. error message is: C:\Documents and
Settings\Owner\MyDocumentsWindowsDefender.msi cannot be found. I have had
Beta 2 since it came out, and it is working fine. Now there is a software
update available and I cannot get it to work. Why am I having so much trouble
trying to get the update? What can I do to fix this problem and get the
software update to install? What happened to the windows defender.msi file?
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Dale