I had to use Mental Ray as the renderer because maya hardware doesn't cast shadows neither calculate occlusion, to help me compose this on the background.
I was able to get the animation working the way I wanted inside Maya as shown in the first image below. However, when I render with Mental Ray, the warriors all render the first image from the loop sequence, like in the second image below. Inside Maya or hardware render, all is correct, the loop is cycled at random start for every particle. I used Sprite Wizard to setup this particles.
I already cached the particles, and tried the export full dag path, in render globals - translation, all without success...
Do I need to set expressions elsewhere to get Mental Ray to render out the correctly?