We have this on the list as RH-87048 Annotation: Hatch: Number of Dashes
There is currently a 300 000 limit on the number of segments that can be displayed in one single hatch object.
For the time being, if you really need that many squares in a hatch, you could create several hatch objects next to each other and set their base point so that they appear to be a single hatch.
-wim