If you create a very dense hatch, AutoCAD may reject the hatch and display a message indicating that the hatch scale is too small or its dash length too short. Wit very dense patterns You may think that an AutoCAD crash has occurred.
Change you hatch pattern scale
You can change the maximum number of hatch segments by setting the MaxHatch system registry variable using (setenv MaxHatch n) where n is a number between 100 and 10000000 (ten million)
The default setting is 10000
To change the MaxHatch setting, on the command line type:-
(setenv "MaxHatch" "1000000")
Important: the text is case sensitive, quotes are needed around Maxhatch and the value and that brackets must be used.
The point of having this setting is to prevent dense patterns from locking up the PC or causing AutoCAD to crash, If the value is raised too high you will also need to consider other users who will be using the drawing.