If you see the following message at the top of an Account:
This Account has one or more invoices that are past the shipping cut-off date.
It is because a user has toggled the "Past Due?" flag for that Account or your organization has enabled automatic flagging of past due accounts (for more information about automatic flagging please see the article: Automatically Flagging Past Due Accounts)
To manually remove the flag:
Edit the Account
Change Past Due? to No and save your changes.