ya i think when i tried using that i got the same error.
just go to your blocks admin and paste this code in a new block
<span id='instantventrilo'><a href="http://www.instantventrilo.com/">Ventrilo Server</a> Hosting by InstantVentrilo.com</span><script type="text/javascript" src="http://view.light-speed.com/ventrilo.php?IP=74.86.15.25&PORT=3764&CHANNEL_WNOUSER=YES&HELP=NO&WIDTH=150&BGCOLOR=333333&STYLE=1&SHOW_IP_PORT=YES&SN_BGCOLOR=000000&SN_COLOR=FFFFFF&INFO_BGCOLOR=660000&INFO_COLOR=FFFFFF&HELP_BGCOLOR=660000&HELP_COLOR=000000&CHANNEL_BGCOLOR=000000&CHANNEL_COLOR=FFFFFF&UN=000000&UN_BG=660000&METHOD=js"></script>
and save it. MAke sure you change your ip and port in the above code. You may also want to play with the colors to match your site. I had no issues with this code and it works great.