Make sure you're on GoZync 5.04 (version history and migration instructions are here).

Then, download the latest version of the GoZync files here:
http://www.seedcode.com/filemaker-sync-gozync/

Update the following two scripts in the your GoZyncMobile file, but don't delete the scripts themselves. Rather, use the "Select All" command to select and delete the entire contents of each script, then copy/paste the updated contents of each script from the new version of GoZyncMobile into the corresponding scripts in your GoZyncMobile file. Here are the two scripts that need to be updated this way:

Zengine ( IDsToSync )
Check GTRR Script

If you will ever need to sync more than 30,000 or so records at once, you'll need to replace your copy of GoZyncHosted with the new GoZyncHosted file from the 5.05 download package. This file contains a new script called "Locked: Set PSOS Result (result)". You'll also need to link the broken Perform Script in "Get IDs Needed For Sync PSOS" in your hosted file (immediately following the If[$length > 999000] step) to this new "Locked: Set PSOS Result (result)" subscript from GoZyncHosted.

That's it!