I would suggest attempting to get s-off via firewater using the temp root method. This should allow you to flash an RUU that has a downgraded hboot, which might fix your problems. Alternatively, if you don't want to get s-off, flash an RUU that has an updated hboot, which should do the same thing.
Thanks. I haven't tried firewater before, so I will have a read up on how to do that. Unfortunately I can't flash any ruu as things are at the moment, because fastboot oem lock command won't work for some reason. I do ultimately want to be s-off though, so I guess I will have to be careful with newer RUU's.
I will post back my results.