Suggestion!
When you ran the SSIS did you try it from Visual Studio IDE? Also when it errored are you running directly from the Server. If so one thing I can think of is the Path that you are giving for the configuration. Is the path to the configuration same in both SQL 2005 and SQL 2008?
I would also try creating a new Configuration file and see whether the package work with that just in case the file is corrupt. It happens if you try opening the file in some XML editor and saving it.
Regards,
Nachi