When trying to edit an existing ADMX Action in Environment Manager relating to Internet Explorer, you may come across an error stating that the ADMX cannot be found and is no longer available, as such you are not able to edit the ADMX.
This issue is seen when the version of the "Inetres.admx" file used for Adminstrative Internet Explorer templates has been updated since the original ADMX Action was created. For example if the ADMX Action was created whilst Internet Explorer 9 was installed, then later Internet Explorer is upgraded to version 11, the upgrade of Internet Explorer will update the version of the "Inetres.admx" file.
When editing the ADMX Action the original "Inetres.admx" file which was used to create the action initially will no longer exist, so the error is seen.
To resolve this issue you will need to recreate the ADMX actions as new.