Windows Defender in Windows 10 displays a window with the message:
"Page not available. Your IT administrator has restricted access to some areas of this application"

There is a rule that only one antivirus program can run on one computer. After installing the external antivirus program, Windows Defender is disabled, hence the above message is displayed informing about the restriction of access to the application. On one computer you can use only one anti-virus program, either it will be an external program, or after uninstalling the built-in Windows Defender

Another similar error very common, which is made by users of personal computers. When the license of the antivirus program is over, the second program is installed Antivirus without first uninstalling. The system is starting to go crazy and really bad things are happening. The worst consequence of this error is the need to reinstall the system.