Image is not loaded sometimes

Hi frnds,

In my webpage , Im using a *.bmp image with the size of 49k.
But it is not loading sometimes.
(i.e,) For my page im retriving the image from the server on the page
onload, Most of the image is loading , but some it is not loading ,
on that time in http analyser shows as image not found (404) error.
I dont know ,why the iamge not loading sometime.

Can anyone tell me reason and how to avoid this thing