Kademan,
Try going here.
http://www.boonex.com/unity/forums/topic/Install-gives-error.htm OR
http://www.boonex.com/unity/forums/topic/allow-url-include.htm - [This one as recent as 5/8/09.]
One thing I've learned about this forum and passing on to you. If you take the error message and post it in the "search" you will most likely find someone has had the problem and a solution provided. I did this with your error message and several postings addressing this were listed.
Another thing, not many of the veterans will respond because they know what I've just stated to be true and consider newbies a pest (or will not be so kind when they do respond) if we do not at least take the initiative to find a solution using the forums' search feature.
Take it for what it's worth but this has been my experience in less than a week. I've done many things on my own by digging and researching. I've also had help, too from a few here, as well.