Not sure what the SSIS is doing inside, But many times people forget that if there are other OLEDB conenctions and and you are accessing other server and databasese then your SQL agent need to have access to that server and DB.

Also, it can be a fire wall issues like in our work environment we have a something called NetSeg, two server cannot communicate if one is outside of NetSeg and other is inside.

Alos, Check if your are usning any password in SSIS and if the SSIS is password protected. This usually creates an issue while running in job.

Error message would be helpful.