Unable to update to newest version of Longhorn

So I am using the Microsoft Beta Client, selecting 'Updates' on the left
sidebar, then clicking on the 'Scan' button. It tells me the following:

"The Longhorn package on your system is out of date. Please click Yes to
remove the out of date version from your system. You will be able to download
the updated version after deleteing the old one. Remove the out of date
version?"

So I click Yes, then a window appears which says "An error has occured with
the Microsoft Beta Client. The error was:"

Then below it says "Unable to delete package. See event log for more
information.
Access to the path 'Accessibility.xml' is denied."


Can someone help me with this? I'd really like to update my system. Thanks!!!!