When you migrate meetings from an Outlook mailbox or PST file to another Mailbox or PST file, meeting requests will be "broken" and you will be missing the "Send Update" option. As a result, you will be unable to send updates to the meeting attendees.
The usual error is that the meeting request is not sent.
The work around is simple:
Move the meetings, don't copy them, don't import them.
To move the meetings, you need to have access to the original data file. If you are moving Outlook to a new computer, copy the *.pst file, don't export it. Unless it was created in Outlook 2002 or older, you can use this data file in Outlook 2003 and up.
- With the original data file on the same computer as Outlook, open it using File, Open, Outlook Data File.
- Open the Calendar folder and switch to a list view.
- Select all and use the Move to Folder command, selecting your current Calendar folder.
See Merging Two Calendar Folders for a tutorial and screenshots. Remember, you must use Move to folder (or drag and move), not Copy.
If you don't have access to the original data file or mailbox that contains the original copy of the meetings, you cannot send updates. You'll need to make a new meeting if you need to make changes to it.