ERROR: Could not allocate memory for 'output_pixels'.
A common error with dmfilth is to use an event file as input instead of an image. If an event file is used event file, the tool bins it into a very large image (8192 x 8192 for ACIS). With an image that large all the system memory can easily be exhausted -- especially if running on a 32bit machine which is limited to ~2Gb of memory per-application (regardless of how much memory is installed).
Ensure that an image is being used (dmlist the file will show either 'Table' or 'Image'). If using a table (ie event file) then it should be binned into an image first.