Sometimes while installing SQL server 2008, you might face some validation errors like Reporting services catalog database file existence failed.
The solution is really simple. follow below solution:
Open the folder
“C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA”
Delete the below 4 files from the folder
After deleting the above files ,click Re-run in the setup window. It should work now. You should
not get any validation error.