Server 2012 NPS recieving unknown authentication attempts from DOMAIN\guest account

hello,

i pretty new technet, appreciate assistance can , forward assisting others in future.  

i have server 2012 nps server setup use radius server wifi users use domain credentials along 802.1x. using ubiquity aps here in our environment. setup nps along self signed user certificate have deployed using gpo various devices.  my setup has been working beautifully, until noticed weird issue yesterday.  all of our aps unifi ap-lr's , have single unifi ap-ac.  it seems randomly when trying authenticate via 1 ap-ac, repeatedly prompted credentials , never able connect. when checking nps server, says receiving connection request mydomain\guest.  however, no 1 trying log in guest account.  does have ideas why be?  below sample of log of problem:

network policy server denied access user.

contact network policy server administrator more information.

user:

                security id:                                            cablebahamas\guest

                account name:                                     -

                account domain:                                 cablebahamas

                qualified account name:          cablebahamas\guest

client machine:

                security id:                                            null sid

                account name:                                     -

                qualified account name:          -

                os-version:                                           -

                called station identifier:                      24a43c52aaa1:rev-corp

                calling station identifier:                     8019349def31

nas:

                nas ipv4 address:                                10.70.1.42

                nas ipv6 address:                                -

                nas identifier:                                       24a43c52aaa1

                nas port-type:                                     wireless - ieee 802.11

                nas port:                                               67

radius client:

                client friendly name:                           rev-corp

                client ip address:                                  10.70.1.42

authentication details:

                connection request policy name:     rev-corp

                network policy name:                         -

                authentication provider:                     windows

                authentication server:                         radius2.cablebahamas.com

                authentication type:                           eap

                eap type:                                               -

                account session identifier:                 -

                logging results:                                   accounting information written local log file.

                reason code:                                        34

                reason:                                                  user or computer account specified in radius access-request message disabled.

thanks reply eve wang,

what ended resolving issue firmware update on ap. assistance eve.

Windows Server  >  Network Access Protection