Chart of Accounts

Upon paying an invoice I  created a new account 6000 but in doing so  I didn't select a Group Account.  My expense accounts are from 5000-5999 so I went back in after posting and reallocated that 6000 account to a 5000 one.  Now I get the error "Accounts are not in logical order; there is a missing...." and I tried deleting the 6000 account but it won't let me, nor will it let me assign this 6000 account to a Group Heading. Upon trying to delete the 6000 account I now get the message: "You have used this account in transactions this year and cannot remove it until the transactions are cleared"!  When I reallocated this expense to the 5000 account the balance is 0 in the 6000 account.  Why won't it let me delete it?  Can you give me some advise??