Invoice Lines

When attempting to see the invoice lines for a purchase order I get the following message The descriptive flexfield with application name Payables (SQLAP) and name Invoice Lines (AP_INVOICE_LINES) is not frozen. Please contact your system administrator I have recompiled the flexfield with no errors but continue to get the message. We have just upgraded from 12.1.3 to 12.2.6 It is working in 12.1.3 Thanks Paul