ISAPI filters detected on the report server site
Upgrade Advisor detected one or more ISAPI filters on the Web site that hosts the report server and Report Manager virtual directories. ISAPI filters are not supported in SQL Server 2012 Reporting Services.
Before upgrading, verify whether the ISAPI filters on the Web site are used by Reporting Services applications. If you do not require the ISAPI filter, you can upgrade the report server. Setup will create the default URLs, without support for the ISAPI filter that runs in IIS. If you require the ISAPI filter, do not upgrade until you find an alternative way of hosting the ISAPI filter (for example, using ISA Server or continuing to host the ISAPI filter in IIS). The report server supports ASP.NET HTTPModules as a replacement for ISAPI filters in certain scenarios. For more information, see the ASP.NET documentation on MSDN.