Security problem with a DTS scheculed


I have a DTS that run weel when I run it manualy I mean when I right click
on it et select Execute DTS.

When I Scheduled The DTS it fails.
The DTS is importing Data From an accpac Application with a SYSTEM DATA
The accpac Files are on another server.
First I was using a Map Drive.
After I try a UNC path.
I test the UNC path and it work ok
I start manualy the DTS and it work ok

The user that run the sql Agent service and MSqlServer is an domain
Administrator user

Soon as I scheduled the DTS it fails with this error message :

Step 'Copy Data from JC65ANME JC CustomerManager Names to JC65ANME Step'

Step Error Source: Microsoft OLE DB Provider for ODBC Drivers
Step Error Description:[SSDB]Path invalid opening user file in SI_AppCreate
Step Error code: 80004005
Step Error Help File:
Step Error Help Context ID:0

I dont know what else I can try

Do you have any idea?
We know that the path is good because the DTS work mhen I start it manualy :)

Thanks in advance!