Error message is:
Rule “Reporting Services Catalog Database File Existence” failed. The Reporting Services catalog database file exists. Select a Reporting Services files-only mode installation.
This issue occurs because the databases for the SQL Server 2008 Reporting Services instance that you want to install already exist on the computer.
To resolve this issue, move, rename, or delete the existing Report Server databases. Or, use a different instance name here %ProgramFiles%\Microsoft SQL Server\MSSQL10.Instance Name\MSSQL\DATA