Install both 32-bit and 64-bit versions of Microsoft SQL Server Compact 3.5 Service Pack 2 on a 64-bit Computer
---------------------------------------------------------------------------------------------------------------
Microsoft SQL Server Compact 3.5 Service Pack 2 has separate Windows Installer (MSI) files for 32-bit (x86)
and 64-bit (x64 or AMD64) Computers. It is mandatory to install both the 32-bit and the 64-bit version of 
SQL Server Compact MSI files on a 64-bit Computer. Installing only the 32-bit version of the SQL Server 
Compact 3.5 SP2 MSI file on a 64-bit computer will lead to failure of the existing SQL Server Compact 3.5 
applications on the Computer. If you are developing an application that uses SQL Server Compact 3.5 SP2 
than you should package both the 32-bit and the 64-bit version of the SQL Server Compact MSI files and 
install both of them on a 64-bit Computer along with your application. 

To ensure proper functionality of all the applications that are dependent on SQL Server Compact 3.5 SP2 on 
the Computer install SQL Server Compact 3.5 SP2 as given below:

Installing SQL Server Compact 3.5 SP2 on a 32-bit Computer (x86):
1. Install the 32-bit version of SQL Server Compact 3.5 SP2 by running the SSCERuntime-ENU-x86.msi

Installing SQL Server Compact 3.5 SP2 on a 64-bit computer (x64 or AMD64):
1. Install the 32-bit version of SQL Server Compact 3.5 SP2 by running the SSCERuntime-ENU-x86.msi
2. Than install the 64-bit version of SQL Server Compact 3.5 SP2 by running the SSCERuntime-ENU-x64.msi

For more information visit http://support.microsoft.com/kb/974247.