Um, ...use a larger hatch scale?
If persistent maybe your MaxHatch setting is low. Type on command line (getenv "MaxHatch")
Mine's set to "10000". From AutoCAD help:
To set the limit of objects in a hatch pattern
At the Command prompt, enter (setenv "MaxHatch" "n")
where n is a number between 100 and 10000000 (ten million). The higher the value, the more dense the hatch pattern.
Note MaxHatch is case sensitive.