This issue because of account which is in invoice, already Deprecated and Odoo not allow to create transaction on deprecated accounts. You need to change active account in Invoice and then you can validate it.

Or you if you want to use same account you need to uncheck deprecated in chart of account to make it active account. 

You should check which accounts are deprecated (Accounting -> Configuration -> Chart of Accounts -> use the filter to select accounts where "Deprecated = True") 

Then check whether each account should have been deprecated - if that is correct you need to change the account used on product categories (etc.), or if it was a mistake then un-tick the "Deprecated" checkbox for that account.    

In the current version of Odoo 12 it displays a message telling you which account is deprecated, which helps! 

First you cannot delete any account which having any accounting entries. So for that reason Odoo providing deprecated mechanism. Normally when you deprecate account then you must have to set another account on replacement. So probably in your case either party(customer) account or product/product category account you set which are now deprecated.  so you need to rectify those accounts.