This is one of those things that doesn’t seem to be well documented anywhere so I wanted to post.
If you are are writing a web app that allows for a download of an ICS file to Outlook and its giving this error when you choose Open:
The Operation failed. An object could not be found.
This mostly occurs with IE6 because of a conflict in the web pages cache setting and how IE transfers attachments to external apps.
You need to investigate your Cache-Control header on the file coming back. Its probably something other than “public”, possibly even “no-cache”. This will cause IE6 in particular not to write the file to disk. So then when Outlook tries to open the file, it can’t find it and gives you the error. Simply setting the Cache-Control header to public will allow IE to write the file to your cache and Outlook can find it.
Newer browsers seem to be smarter about this and allow no-cache items to work correctly regardless.
So now you know — maybe once IE6 is dead and gone the world will finally be a better place.