TCP/IP stack corruption

Hi all,
   
    I am working on at91rm9200 board. This board has Micrel ethernet controller on it, when I assign the static ipadress to this interface then board is respond to the ping commands for some time and after that all the ping requests to the board are getting timeout. Help me in getting could be the problem in this scenario.

Other problem is the if the size of the code increases in my application do_dhcp function seems to hanging which is getting called init_all_netowork_interfaces(DHCP enabled in this scenario).

Thanks,
Neeraja