Finally got around to looking at this again after a break of 1 month. Before attempting suggested solution I tried a normal upgrade again and, hey presto, it worked. I can only assume that when the upgrade failed the first time, NS&R must have been doing something in the background which it wasn't doing this time.
mumford68 wrote: I don't know if it had made any kind of differnce but I believe that 360 went through a couple of small changes from version 3.0.0.134 to 3.0.0.135.
The only difference in them is the search box in the Norton Toolbar. Some localized versions do not have it, they are version build 134, and the versions that have the search box are 135.