The Electrostatic Diamond belts are formed on a thinner paper backing instead of the typical cloth backing found on silicon carbide belts. This means that they may require a slightly higher tension on the belt sander in order for them to track correctly.
Be careful not to increase the tension on your sander too much as you don't want to overly stress the joint and cause premature failure.
It's important with thinner belts like this that you have a crown on the drive wheels on your sander. If you have an older sander, the crown may have been worn down over time and you'll have a harder time tracking with this thinner belts. You may need to re-machine your drive wheels, or replace them, or use masking tape to create a crown in the center of your wheels again in order to track these belts correctly.
I'm having a hard time getting my Electrostatic belts to track correctly, what's wrong?