Unfortunately I do not have BIDS 2K8 at hand so I'm going by my gay cell memory here (which has a high number of bad sectors). If you select the package in the solution explorer and press F4, you get the properties of the package. Down at the bottom there should be some stuff about security, what does that say?

The other thing is, have you tried to RDP (Remote in to) the actual server and using the simplest of means (command line or any file transfer software) connect to the file server from where you are pulling the files from. Of course you will have to test this as the windows user in which scope the package runs.

😎