I have a clean copy of Windows Server 2008 R2 64-Bit. I downloaded 2 files from Microsoft: SQL Server 2008 Express w/ Advanced Tools (SQLEXPRADV_x64_ENU.exe) & SQL Server SP1 (SQLServer2008SP1-KB968369-x64-ENU.exe). Both of them are the 64-bit version. I installed the Basic Engine that installation and then SP1. They both worked fine.
The problem occurs when I want to add another feature, let's say Full Text search. I open up the SQL Server Installation Center and then click the Install & Add Features link in the Install submenu like I did when I first installed SQL Server 2008. When I did that, I revived an error message that says Object Reference Not Found. At this point, I decided to run SQLEXPRADV_x64 again but the same error occured. At the same time, I went to the Uninstall Programs in Windows 2008. When I clicked Uninstalled the same Object Reference Not Found message appeared.
This basically means I have a one-way time limited permanent install. For the most part, I had better know what features I want installed because after that initial installation - I cannot upgrade or uninstall anymore. I also tried the same with Web Platform Installer. It installed SQL Server Express w/ SP1 but failed in installing Management Tools as an after-feature.