[Plugin: AdRotate] Banner's link take mydomain.com as a prefix

Hi! I dunno why this is happening, I followed all the instructions from the support @ plugin’s homepage. For example, I want to redirect people to the advertiser’s webpage when they click on the banner, and the plugin sets the target to http://www.mydomain.com/advertiserwebpage.com
Sorry if my english is quite hard to understand. Hope someone can tell me what am I doing wrong. Thx!

http://wordpress.org/extend/plugins/adrotate/