IS your hatch to dense???
Auto-cad sets a default limit of hatch segments to 10000. So if your hatch has more segments than that Auto-cad will not create the hatch. You can change this so that you can get a more dense hatch when needed.
Key In the following command line to modify this setting. note that this key-in is case sensitive and you must include parenthesis.
(setenv "MaxHatch" "10000")