The first thing I would look at is whether he has a personalization on the Part Tracker form. if so, Delete his personalization (Customization Maintenance) and have him log out of Epicor and log back in. (From time to time the personalizations get corrupted). (Also clear his client cache on the computer he uses most often).
If that doesn’t resolve the issue, the second thing I would check is the Menu Maintenance security settings for that the Part Tracker he is trying to launch - if it’s limited to specific security groups, make sure his User Account has one of the Security Groups that it is restricted to.