There are two possible reasons: The first one is the setting of your adjustable brackets. If you are using the correct bolt adapter, but the 19” rail doesn’t fit, you would need to adjust the brackets. Find out to do so here. The other possibility is that you are using the wrong bolts. The Setup.exe is compatible with threaded holes as well as square punched holes. By default, it is equipped with bolts for square punched holes. If you have a network rack with threaded holes, you first need to change the bolts.
Loosen the bolts on both brackets with a wrench (10mm or 3/8″) and remove them.
Now take the other bolts and put them in the holes.