DTS Package fails to find import file from c# app

I posted this to the SQL Server group but got no good responses, so I'm
trying here...

I have a DTS package I am kickig off from a C#.Net applcation that imports a
tab delimited text file created by the C# app. I can successfully kick off
the DTS package from my development machine, run the package, and everything
works great.

When I install the app on another machine, it successfully kicks off the DTS
package, but the package fails to find the text file to import. I am pretty
sure this is some kind of permissions issue. I am using SQL Server security
rather than widows security on the login to the SQL Server. The file name is
referenced using the UNC filename (although I have also tried the direct path
to the filename on the server with the same result). Any ideas why this
would perform differently on two different machines (even when logged in
using the same network account)? What security account
does a DTS package kicked off from a client machine run under?

Thanks in advance for any help.