Yahoo! Messenger voice call & video call disabled, why?

Was trying to help my colleague to troubleshoot her laptop, where the Yahoo! Messenger voice chat & video chat are disabled even though the setup of the sound & video are all correctly configured.  Yet, it will still throw the error message "Your computer is not connected to the network", which is quite amazingly considered that the wireless network is working plus the Skype is able to make the call.

After several finding on the Internet and on some help site, non of the solutions are able to solve the problem.  Then I recalled the other colleague is also using the same laptop and her Yahoo! Messenger is able to use video call & voice call.  I was guessing the whole time of what could be the possible cause that hers is working but not this one.  Then a thought came to my mind, could it be the firewall?

The firewall is correctly configured, so what else inside there that is blocking the connection?  The other security software that's installed is the Trend Micro Client Security Agent, which has already been disabled, but has not been removed.  So I asked the other colleague whether she has uninstalled Trend Micro from her laptop and she said yes, so I thought maybe give it a try since it's an evaluation version.

Yet, removing the Trend Micro is not that smoothly either due to the system not able to remove everything, which caused me to have to remove some of the components manually.  After everything is done, I reinstalled the Yahoo! Messenger, and this time, voila!!!  Everything is working, the voice chat, the video chat & everything related to voice in Yahoo!  Messenger.

This is pretty weird considering that by disabling the Trend Micro, one would perceive that such would not cause any issue to the firewall setting, but it turns out not really the case.  Could it be because that the security agent would still run in the back ground even though it has been disabled?  That could really create quite a lot of unpleasant experience to end-user.