AES 721 running on Platform 721/722 can receive messages from Platform 7.4. There are alert codes from platform 73 and 74 that AES 721 will log but not interpret.
We strongly suggest that you consider the FREE PDC service in place of AES. PDC service supports platform 63 - 81 and is enhanced every week or two. Happy to do a demo for you - I think you'll be very impressed by PDC.
To continue running AES on site, upgrade to AES 7301 on platform 74. There are hotfixes required for AES 73 user interface to render properly on platform 74