I have had this error message when attempting to run a dts package connecting to Oracle when the package was designed on a computer with the Oracle drivers but I was attempting to run it from a computer that did not have the Oracle drivers.   Could you be running the job from a different computer than the one that developed the package?

Also, I have just gotten through dealing with a similar job problem (ultimately caused by Oracle permissions changes between versions) which was only resolved by creating a .bat file that used DTSrun and then scheduling the .bat file in Windows AT Scheduler instead of using the SQL Server Jobs Scheduling.  Perhaps that might help you?  The syntax is

DTSRUN /S "<servername>" /E /N "<packageName>"

Where <servername> is your SQL Server, and <packageName> is the name of your DTS package.  Just put this in a text file and save it as a .bat, then run the .bat from either [Start]/[Run] or the command prompt.  If it works, then schedule it from the Windows Control Panel (Add Scheduled Task).

Good luck,

Metra