Differences btwn Pre Render MEL and Pre Render Frame MEL

Maya
1

"polyCube;"  -- when i put this statement in Pre Render MEL, its shown in render. But when put it in Pre Render Frame MEL, it doesnt shown.
WHY?! is there any issue in my Maya?

In general,
What are the differences btwn Pre Render MEL and Pre Render Frame MEL, other than the 1st one executes only at start frame and the 2nd, for every frame ?

2

yyou rendering in mentalray? Well it may be too late to affect the exoport since it was done allredy.

3

i'm rendering using Renderman, in Maya 2008.

4

.. and this problem is only in Batch render and only in Renderman render. No issue when do 'Render current frame'. It works fine using Software render in batch render also.