hey this time i go to bios setting then in my video configuration setting i decrease this to 128 MB..
means less the part that taken from my ram now when i render my FG pass it render some part of it but then my maya got hang....

n I can't see the details in the script editor...

but in the output window it shows..
MEM 0.3 fatal 031008: can't allocate 18405588 bytes.