I have seen this happen, we moved a cusomer's Norstar to a new building which was in a location which required them to use a new Telco provider. That's what we thought was the issue however when we'd check the lines using a test set, the lines rang in properly. ITAS said they had never heard of this happening, we too tried to reboot the system and nothing seem to work. Our customer just finally accepted it, although they didn't want to because everything worked ok at the old location. I guess what I'm trying to say is I don't know of anyway to resolve this what we didn't try was a different KSU, but if you have one or can get cheap I guess it wouldn't hurt to try. Let me know if you find a way to fix this.
Good Luck