Can't install ajax search plugin

Hi,
I just bought the Ajax Search Pro plugin, and tried to install it via FTP. I uploaded the ajax-search-pro folder into the ‘plugins’ directory, and Activated it from my Dashboard. When I did, my site stopped working. It displayed a ‘Fatal Error….etc, etc.’ message in my browser. So I went back into the FTP and deleted the ajax-search-pro folder.

Then when I went back into my dashboard, I got a message saying that the plugin was deactivated since it could no longer be found. I then tried to install it via the dashboard, by going to Plugins, Upload New. When I uploaded the zip file, it did not show up in the list of plugins, so I can’t activate it. That’s where I am at now. It seems that I am unable to install the plugin sucessfully. Can you help me?

Thanks, Dave B.