msdn.microsoft.com/en-us/library/ms141766.aspx
Selecting 32-bit or 64-bit Package Execution in SSIS Designer
In the Project Properties of an Integration Services package, you can select 32-bit or 64-bit execution by setting the value of the Run64BitRuntime property on the Debugging page. By default, the value of this property is True. When the 64-bit version of the Integration Services runtime is not installed, this setting is ignored.