When you want to see if a Setting exists, you really need to also check to see if the “Value of” the setting exists.
This is because when a setting is “deleted”, the value is deleted, but the setting itself still exists. So try something like the following …
(version of client >= "126.96.36.199") AND ((exists true whose (if true then (exists setting "__Group_0_No Shutdown" whose ((exists Value of it) AND (value of it as lowercase is "true")) of client) else false)) AND (exists true whose (if true then (exists (operating system) whose (it as string as lowercase contains "Win" as lowercase)) else false)))
Also be sure that you do not use “magic” quotes. The relevance you posted used them (Left and Right hand quote characters, endemic of products like MS Word). You need to be sure that you only use the plain " character. You can validate your Relevance using the Fixlet Debugger (aka QnA).