"MsDrawMap():Failed to Draw Layer" Error

[Chris Hodgson]

I'm getting the error:

"MsDrawMap(): Failed to draw layer named 'orthophoto'.

Sometimes, depending on where I happen to be zoomed in to. Here is my
layer definition:

  LAYER
    NAME "orthophoto"
    METADATA
      "wms_title" "orthophoto"
    END
    STATUS ON
    TILEINDEX "tiles.shp"
    TILEITEM "Location"
    TYPE RASTER
    PROCESSING "BANDS=1,1,1,2"
    PROJECTION
      "init=epsg:42102"
    END
  END

I'm using Mapserver as a WMS 1.0 server, and my image files are
greyscale jpeg-2000 files with an alpha channel. The tileindex was built
with gdaltindex, and all the files were created with gdal as well. It
works fine in some areas, and not in others.

How can I find more about the cause of the error? I looked in the apache
error_log, nothing there. I tried turning DEBUG ON in the mapfile, no help.

Thanks,
Chris