Error Sales tax code must be entered if account number is a sales tax account.

Dear all,

I find an error when posting in general ledger

In general ledger i input the journal

Vendor (DB) 1000

Vat In (CR) 1000

When posting the ledger i got the error 

"Sales tax code must be entered if account number is a sales tax account."

Does any one can help me ?

Thanks in advance

Regards

Rudy