Random reboot while tcp-ip file transmission

i would like to add some details :

-> my app is a mix of c++ and c

-> My app is located on a nfs drive.

-> In the beginning, I allocate 4Mb with mmap but I never free it because I stop my app with kill -9. I don't think it can be the reason of my problem ; can it ?

-> I have 32 Mb of memory and my app takes 4973 (says ps)

It seems that when I change the romfs and when I upload it to the board, my app always behave ok.

When I put on my board after a few hours it has been off, my app seems to beahave also ok.

If it's memory problem, what can I do to detect it ? what tool can i use ?

thanks,

Cedric