I've created a custom hatch pattern of a grid that I can easily scale to match the spacing of the lines and placed in the appropriate "Library" folder.  When I try to place the hatch pattern in the drawing, the named pattern does appear in the Hatch Library as a square with a cross through it (apparently not a good sign).  When I choose it and a point in the drawing, I get "Error in Pattern mzatile.  What would you like to do with this pattern?"  I've created custom patterns before (and this was edited version of another), but this one is failing:

;; <- Begin mzatile ->
;; MZA tile elevation
*mzatile, MZA tile
0, 0,0, 0,1
90, 0,0 1,0
;; <-End mzatile ->
;;

Is the file name and pattern name case sensitive?  I've tried both ways.  What else might I be missing?