Issue:
The disable button on the Customer Free Text Invoice is disabled for a user which has the CustFreeInvoiceMaintain privilege assigned.

Summary:
This situation only occurs in Ax2012 as Ax2012R2 has made a change to the CustFreeInvoiceListPage entry point within the CustFreeInvoiceMaintain privilege of setting the Access Level to delete from read.

Workaround:
In Ax2012 open a developer workspace
- Open the AOT
- Navigate to Security - Privileges - CustFreeInvoiceMaintain
- Expand CustFreeInvoiceMaintain, select Entry Points - CustFreeInvoiceListPage

In the properties change the Access Level from Read to Delete