'Microsoft.ACE.OLEDB.12.0' provider is not registered -but it is

Question

Short and sweet:

• app works on x86 machine but not on x64 (tried on a 2008 Server and a Windows 8)
• Microsoft Access Database Engine 2010 already installed (also have Microsoft Office 2007 Access Database Engine installed)
• MS Office not installed
• confirmed the existence of C:\Program Files (x86)\Common Files\microsoft shared\OFFICE12\ACEOLEDB.DLL

Code:

string conn = "Provider=SQLOLEDB;Data Source=localhost;Initial Catalog=Northwind;Integrated Security=SSPI;";
OleDbConnection _connOle = new OleDbConnection(conn);

Any ideas what I should do to get this app to work on the x64 machines? Thanks!

Solution

I can think of two scenarios that could explain your issue:

1. Your C# project is set to target both 64-bit and 32-bit platforms and the 64-bit machine has only the 32-bit version of the Access Database Engine installed. The reference fails because the program is running as 64-bit but the machine is missing

   C:\Program Files\Common Files\Microsoft Shared\OFFICE14\ACEOLEDB.DLL

2. Your C# project is set to target 32-bit platforms only (x86) and the 64-bit machine has only the 64-bit version of the Access Database Engine installed. The reference fails because the program is running as 32-bit but the machine is missing

   C:\Program Files (x86)\Common Files\microsoft shared\OFFICE14\ACEOLEDB.DLL

Note that the installer for the 64-bit version of the Access Database Engine installs just the 64-bit version, not both.