I have an integraiton package that I created in VS2005.  It has worked fine for many months.  I recently opened it to make some changes and all of my connecitons to an excel spreadsheet were throwing errors:
"The AcquireConnection method call to the connection manager "Excel Connection Manager" failed with error code..."

I had recently installed VS2008 and other software -it could have been one of those causing the problem - it's hard to tell.

Turns out the solution is this:

1. Open the properties of your integration project.
2. In the Debugging section, change the value of "Run64bitRuntime" to false.

SSIS 2005
Sql Server 2005 Integration Services
VS2005