Answer by Dave Myers

My first impulse would be to look for 1 of 2 things. The first has already been stated once, and that is that some other process (to include maintenance jobs) may be accessing the database at the time your package is attempting to do the insert. The other , based on the fact that you say you can run the job manually without failure would be permissions. Whenever you run the job manually, it takes on your permission set (which I would assume would be sa), but the job owner may not have sufficient permissions to perform the actions on the database. I would double check your job owner permissions