To show detailed Error Messages on a IIS 7.5 (Windows Server 2008 R2) for Classic ASP sites, add the following tags in the web.config.
<system.webServer>
<httpErrors errorMode=”Detailed” />
<asp scriptErrorSentToBrowser=”true”/>
</system.webServer>
<system.web>
<customErrors mode=”Off”/>
<compilation debug=”true”/>
</system.web>