How frozen the Descriptive Flexfield for invoice payments named AP_PAYMENT_SCHEDULES

Hi everybody
Attempting to pay an invoices batch after click on start action not shows the check box under Select option
and  display an error:
The descriptive flexfield with application name Payables (SQLAP) and name Invoice Payments (AP_PAYMENT_SCHEDULES) is not frozen. Please contact your system administrator

and the process stop
How can frozen that descriptive flexfield?

Thanks in advance

Jose Vaca