A financial year cannot be closed off if there is one or more things to resolve in either the financial settings, the chart of accounts, or report layouts.

Check your Retained Earnings and Current Earnings GL Accounts here. Edit and save the GL Accounts to ensure they have the required settings. 

Check that your Profit & Loss and Balance Sheet Layouts are valid. Go to Financials > General Ledger > More Options > Reports. 

If you have any warning signs, edit your Layouts to correct for any recently added or ungrouped GL codes. 

Check your notifications for any other settings required.