Without knowing what the other accounts are in the same area, it's hard to tell you what to do. Basically you violated the rules of the chart of accounts. Each group of accounts has to have an H at the top and T at the bottom. G and A accounts can reside between the H and T but any subgroup of A accounts must be followed by an S account before a G or T account can be inserted. If your accounts don't follow these rules, then you get the error. Not knowing what the accounts currently are, it's hard to tell you how to fix it but you can change the number of an H, T and S account if there is room.
BTW, you can't delete an account unless it hasn't been used in the current or previous fiscal years and it isn't being used as a linked account.