Adding Trendmicro to the trusted sites list is sometimes needed in order to complete an online scan.
To do this, we open internet explorer, and click "Tools"
Then we click "Internet Options"
Now, click the "Security" tab (1), and then the "trusted sites" icon (2). The "Sites" button will be clickable now, click it.
Simply type "http://trendmicro.com" into the box as shown, uncheck the box, and click "Add" and then "Ok"
Now, finally, close all Internet Explorer windows, and restart it to apply the changes.
Trendmicro's housecall scan should now run for you.