Meaning of error message"Object open failed because 'Name' key value of 'xx' was not found"

Last Friday November 17 suddenly ran into an error where ZPM would issue an error saying:

ERROR! Object open failed because 'Name' key value of 'xx' was not found

I googled but found no specific help. Step by step I was able to conclude that:

1. This is the error message for error 5770, also known as $$$KeyValueNotFoundOpen.

2. In objectscript, this error can be raised by calls to NameOpen, where 'Name' is the first quoted part in the error message.

3. The error status is raised when there is a call to ##class(yy.zz).NameOpen("xx", , .sc) where yy.zz inherits from %Persistent and has an index named 'Name" and value "xx" does not exist in that Index.

See also https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls... and
the file %occErrors (you have to #include it)

It looks like there is a namespace switching issue in my case.

I though posting this might be helpful for a broader audience dealing with this rather unclear error message.