Yes, Polling Mode (Samba Compatible) is checked.
I will test the file write later today. It sounds like you are suggesting that the userid needs write permissions to monitor a file for triggering? I'm pretty sure the userid that this job runs under only has read permissions, we don't currently have any jobs that write back to the Iseries, but I will create one to test.
Also I do have similar jobs that trigger off of files on Windows shares without issue.