Do you and your opponents have the Cepheus Compatibility Pack downloaded? (it's free) Besides that, only thing more I can think of is.... Did you install SC5 to the harddrive? I wonder if doing that on Xbox can cause problems... (or maybe NOT doing it results in problems for some reason)
I'm playing on PS3, I have it installed to the harddrive, and I do have the Cepheus Compatibility Pack downloaded. I have never not been able to see my opponent's CASs, and to my knowledge they have never not been able to see mine either.
I don't think it has anything to do with the Cepheus Compatibility Pack because it happened even before I downloaded it. Also, I don't think installing it would cause a problem. Sigh....... Thanks for the suggestions though :D