Your 2100 account nbr is your Account Payable and is linked to your sub-ledgers which are your suppliers.

You cannot use Acct nbr 2100 in a journal entry. Every time you make an entry in the purchase module or the payment module this also makes an entry in your 2100 Acct Pay account. If you were to try to make an entry thru the 2100 Acct Pay account without using the purchase/payment modules then you would get a data integrity error. To see if you have any data integrity errors go into Maintenance then scroll down to Check Data Integrity, click on that and another box will open up and at bottom it should say 'Data OK'.

The upper portion is split between left and right and shows how each section on the left balances with the same section on the right.

You need to call your accountant and find out which suppliers need the corrections and then post that thru the purchase module.

In addition to what Smithco said above:

Some accountants use worksheets that add up the net value of Accounts Payable, without taking into account that some pre-payments are a separate asset, not a negative liability.

Pre-payments may have been netted against / combined with payables for presentation purposes, and your accountant may not have intended that the balance be adjusted.  

I had started with a company and accounts payables 2100 not match the a/p report. To fix it I had to temporarily unlink it from Setup/settings/payables/linked accounts. (change 2100 to anything else in the dropdown menu ) do the journal entry and then go back in to payables and re link it. MAKE SURE you dont do any other entries in between or it will screw it all up!