These days, while working on SSIS 2005 (SQL Server Integration Services), I came across a porting issue. My SSIS packages ran fine on my 32-bit dev-box. But as soon as I ported them to 64-bit deployment machine, I started getting errors on connection managers, my connection managers could not connect to the respective data sources.
The thing to note here is that though the 64-bit editions of Microsoft SQL Server 2005 include Integration Services, some Integration Services features are available only in 32-bit versions, or have limitations on 64-bit computers. For one thing, the ODBC, OLEDB and drivers for Office 12 files have a different 64-bit version. So, if you have tested your SSIS packages (and the connection managers there-in) on a 32-bit machine, they might not behave similarly on 64-bit machine.
For the SSIS packages that really don't make use of the 64-bit processor, the SSIS project property Run64BitRuntime can be set to False. This is a instruction to load 32-bit runtime environment rather than 64-bit, and your packages would still run without doing any plumbing work. The property can be found under SSIS Project Property Pages -> Configuration Properties -> Debugging.
You can find more information on 64-bit Integration Services considerations here