Zero2Cool, yes the following setting should be true:

<add key="YAF.EnableURLRewriting" value="true" />

And we must restart the web app to apply it - just changing the app.config file isn't enough ;)

Here's the config file. Do i need to restart the whole iis? i just changed the app config and edit the web.config.

<appSettings>
<add key="YAF.BoardID" value="1" />
<add key="YAF.EnableURLRewriting" value="true" />
<add key="YAF.UrlRewritingFormat" value="standard" />
<add key="YAF.URLRewritingMode" value="Translit" />
<add key="YAF.UseSMTPSSL" value="false" />
<add key="YAF.DatabaseObjectQualifier" value="yaf_" />
<add key="YAF.DatabaseOwner" value="dbo" />
<add key="YAF.ConnectionStringName" value="yafnet" />
<add key="YAF.ProviderExceptionXML" value="ProviderExceptions.xml" />
<add key="YAF.AppRoot" value="~/" />
<add key="YAF.ProviderKeyType" value="System.Guid" />
<add key="YAF.MobileUserAgents" value="iphone,ipad,midp,windows ce,windows phone,android,blackberry,opera mini,mobile,palm,portable,webos,htc,armv,lg/u,elaine,nokia,playstation,symbian,sonyericsson,mmp,hd_mini" />
<add key="YAF.RadEditorSkin" value="Black" />
<add key="YAF.UseRadEditorToolsFile" value="true" />
<add key="YAF.RadEditorToolsFile" value="editors/radEditor/toolsFile.xml" />
<add key="YAF.ConfigPassword" value="12345" />
<add key="YAF.BaseUrlMask" value="http://ForumWeB/CheckForum/" />
</appSettings>

I encountered 404 error. Page cannot be found when i tried to change from standard to advanced.

by the way the hosting setting for the URL used is http://ForumWeB/CheckForum

Here's the URL for Advanced setup
http://ForumWeB/CheckForum/topics/2-Installation-Forum

Here's the URL for Standard
http://ForumWeB/CheckForum/yaf_topics2_Installation-Forum.aspx

<add key="YAF.AppRoot" value="~/CheckForum" />		
<add key="YAF.BaseUrlMask" value="~/CheckForum" />
<add key="YAF.ForceScriptName" value="default.aspx" />