web server demo program using de2_115 kit

If you have a look at the network_utilities.c file you will find functions that give the kit's MAC address. By default when you create a web server demo application, the created functions in network_utilities.c expect to find a parallel flash called EXT_FLASH, and read the MAC address from there. It's possible that your kit uses a different flash, or a flash with a different name.

You should have some example applications that were delivered with your kit. You can copy the network_utilities.c file from those examples, or edit the file yourself so that it doesn't try to read from the flash but return a fixed MAC address instead.