I have faced this problem several times while installing between SQL Server 2008 R2 standard and enterprise edition. The solution to the problem is that after un-installing the current instance of SQL Server 2008 on your machine, reboot and then remover SQL Server 2008 path from environment variables. Then reboot again and install the SQL Server native client (you will be prompted for that while you run SQL Server R2 2008 installation) because without native client you wont be able to install SQL Server R2 2008 properly.
Check for automatically configuring SSRS...If the error persists, restart SQL Server 2008 installation and this time check configuring SSRS manually checkbox.
Hope this helps!
Regards,
Rafayz, Information Management Practice,