Did you dowload the A-CEP here on OFPEC or from Armaholic? If its from armaholic re-download it from here (first post) as this is the newer version of it and some problems with unit caching was fixed. I'm too lazy when it comes to update my packs on all sites...my fault.
However, what was the zone size u used? Did you make a Mission or just some tests with the A-CEP with very small zones?
Once the group is created, the caching routines no longer takes zone center as reference but the actual position of the group leader. The distance the group is restored should be a little smaller than the zone size (just a few meters) and the caching distance should be similar to zone size.
So if you have a zone with size of 100 as example, you stand close to its boarder and the groups are created, one close to you, the other on the far edge of the zone, the group near you should not delete units (you're closer than 100m from them) for caching but the far group will (as the distance is bigger than 100m).
This is how it SHOULD work. If it doesnt and you're sure you have the latest version (no need for editing scriptcalls, 100% compatible) a screenshot of the error and a sample mission (editor version please, not a .pbo) would be nice. As i said, never heard of that error before but this means nothing.
Awaiting your informations to track down this ugly bug.