YUI tabs are used extensively in mojoPortal at the moment. Even if you set AlwaysLoadYuiTabs=false, it will still load them where they are used in admin and edit pages. It does not mean never load YUI tabs.
Make sure you have not changed this to false:
<add key="UseGoogleCDN" value="true" />
With this as true it will load the YUI scripts from google cdn which is why you must be connected to the internet.
The error seems like it is not loading the YUI scripts or they have an incorrect url. You should view the source of the rendered page to determine where the scripts for YUI are loaded from and whether the url is correct or not. If the script fails to load you will get errors.
You can disable all of YUI like this:
<add key="DisableYUI" value="true" />
but then you will have a very ugly admin UI
Hope it helps,