Unable to update security in Vista

Hi. My Vista Home Premium system has started telling me it's unable to
automatically update the security centre. When I try to manually update that
fails to and I get an error message saying Windows cannot find
'::{26EE0668-A00A-44D7-BEB064C98683}\5\::{36EEF7DB-88AD-4E81-AD4...\[ageSettings'.
I also can't update Windows Defender, it says The program can't check for
definition updates and it says "Error found: Code 0x80080005.
I'd appreciate any ideas. David