adrotator

I am totally confused, I spend 1.5hrs on this:
 
can you tell me what is the difference between these two lines?
 
 <%--<asp:AdRotator  id="myads"  AdvertisementFile="Advertisements.xml" Target="_blank" KeywordFilter="Business" runat="server" />--%>

  <asp:AdRotator id="myads" AdvertisementFile="Advertisements.xml" Target="_blank" KeywordFilter="Computer"  runat="server" />
 
Because the comment code will not work and the other one it does. I am confused here
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