I changed the package to DelayValidation and the job now works OK (last 3 days). This doesn't make any sense to me, since the package was failing at the 4th step (when it needs the connection to the iSeries). Without DelayValidation, the job obviously succeeded at the initial validation before starting the package execution.

Just for "fun", I made a copy of the problematic package (without DelayValidation, and just changed the target of the data transfer step to a new table (same format as the production table), and scheduled a job to run this package every 1/2 hour. This job has been running fine every 1/2 hour for the last 4 days. Could it be that the original package is somehow corrupted so that it sometimes works and sometimes fails?:unsure: