How do I change the email address used by Calendar to send invitations?
Standard way:
Go into Mail preference with
Mail > Preferences > Composing
and then change the following option: “Send new messages from”
If this did not work:
Go into Contacts and create a new card or pick the one with the mail address you want to use (i.e. your work e-mail).
Afterwards, go to the Card menu and select “Make this My Card”.
This mail address should now be your default for Calendar.