Sage ACT! 2011 hot fixes are cumulative, so the latest hot fix will include the benefits of all earlier hot fixes for this version. It is not required to install earlier hot fixes prior to installing the latest hot fix.
However, you do need to install the SP1. Thanks to Mike Lazarus @ GL Computing for his blog article, which I've blatantly stolen to post :-)
Important: You must apply this hot fix to all machines that share the database – especially when using synchronization. This includes all machines that contain the Main Synchronization Database (Publisher), Main Remote Database (Subscriber), and machines that have the ACT! Network or ACT! Internet Sync Services installed. All machines must have this hotfix applied for synchronization to continue. Check installed version by going to Help and About Act!. Consult with your administrator before applying this in a sync environment.
