If I remember correctly (I do not have MaxExchange available to me) you keep getting that because the packets in question aren't showing up. For example if packet 17 is missing and you get 18, 19, etc. you'll keep getting that message until 17 shows up regardless if still process the later packets. I believe there is a file somewhere telling you packet number info, but I don't recall what the name is.
You could send a refresh from the main site, but that will completely wipe out the receiving site(s). Any changes made between the last update and the refresh will not be sync'd. Additionally the information in the problem packet will not be sync'd either, but it appears that the users probably don't know what that is anyway.
