No AAA accounting failed

[pacionet]

In a cisco switch WS-C2960X-24TS-L with this firmware

Cisco IOS Software, C2960X Software (C2960X-UNIVERSALK9-M), Version 15.2(2)E7, RELEASE SOFTWARE (fc3)

I am trying to run this command:

(config)#no aaa accounting system default start-stop group tacacs+
                                                                     ^
% Invalid input detected at '^' marker.

Instead the command:

(config)#aaa accounting system default start-stop group tacacs+

works fine.

Any hints?

[MHM Cisco World]

Sorry don't get it 

First command use NO and second without NO?

MHM