Sounds like you have account 1120 linked as the Purchase Prepayments account in the Payables module.  This is usually for a company that wishes to get a retainer or deposit before they complete a job and is usually entered through the Prepayments option in the Payments module.  You have not indicated if the amount should be associated with vendors.  I am assuming your Data Integrity from the Maintenance menu is out of balance right now.

If these are typical Prepaids (eg. a yea'rs worth of insurance paid in June for the next year), then you need to create a new account for Purchase Prepayments and move the link from 1120 to the new account.  I assume the Purchase Prepayments are supposed to be zero when recommending this.

If Purchase Prepayments are supposed to be higher than zero and one or more vendors are supposed to show a prepayment on their history, you will have to do a workaround because the program does not have the ability to enter Prepayments in History mode.  One way to do this is to enter a negative invoice on the same date as the original prepayment (or the last day before using Sage 50).  Then adjust the Opening Balance of the Accounts Payable account on the Balance sheet to match the original A/P and subtract the amount of the Prepayments in total.  Make a note on your setup reporting that you combined the two accounts.