Building a firmware

I'm using the firmware modification kit available on google code to build a firmware, but its not building properly i guess because when i upload the original firmware onto the router it works but when i make changes to the firmware and build it and upload it on router it doesn't work. I'm not getting any errors but my firmware is not uploading properly onto the routerafter i build it. I'm using Linksys WRT54G router and DD-WRT v24 micro generic firmware.
Someone kindly help me