It seems like this is his first time jailbreaking so I doubt he would have his 4.2.8 SHSH saved. Like the eddieg said, it is not currently possible to jailbreak 4.2.10
Yes, I was talking about you, unfortunately since you didnt save it while it was being signed, there is no way to save it now, you will have to wait for iOS5 to be released and jailbroken or MuscleNerd to add tethered support for 4.2.10