By default, in Windows Internet Explorer 7, DEP/NX is disabled for compatibility reasons. Several popular add-ons are not compatible with DEP/NX and fail when Windows Internet Explorer loads them with DEP/NX enabled.
Typically, these add-ons are built by using an older version of the ATL framework. ATL 7.1 and earlier versions are not designed with the DEP security feature. Fortunately, new versions of Microsoft Windows service packs have new DEP/NX APIs that enable you to use DEP/NX and retain compatibility with older ATL versions. These new APIs enable Internet Explorer to opt into DEP/NX without causing add-ons that are built by using older versions of ATL to fail.
When an add-on is not DEP/NX-compatible and it does not use an outdated ATL, you can use a Group Policy option to opt out of DEP/NX for Internet Explorer until an updated version of the broken control is deployed. Local administrators can control DEP/NX by running Internet Explorer as an administrator and by clearing the Enable memory protection option in the Advanced pane of Internet Options.