The relevant registry entry had an unexpected item named 'command':
Code: Select all
[HKEY_CLASSES_ROOT\VueMinder.exe\shell\open\command] @="\"d:\\FolderPath\\VueMinder.exe\" \"%1\"" "command"=[random text that looks like a password] "%1"
On a whim I tried renaming the 'command' key, so that whatever process might have been looking for it would be unable to find it.
Lo and behold, double-clicking the .ICS file opened the Import Events dialog!
Deleting the 'command' item would cause the same positive effect, assuming the item actually serves no purpose.