I have just taken over the accounts and when I try to do error checking the system just tells me to restore. I don't know how far backthis goes but it is at least 12 months. As restore isn't much of an option how do I go about fixing errors?
AFAIK even in the most serious of errors you always have the use of recovery tools, albeit, Sage says, in conjunction with Sage technical support. Probably won't cover every situation, I suspect, so depending on the error perhaps a restore is the only option - corrupt data files, for example.
It all depends what the errors actually are - is it something you can manually sort out with your bookkeeping knowledge - it'll probably mean entering journal entries to make things what they should be. So the first step is to work out, as far as you can, what things should be.
Assuming your client doesn't have Sagecover (I think it's called). If they do, pass it all over to them!