[U-Boot] help: Can't enter thee lowlevel_init.S?

HI: i port the uboot-2009.06 to arm2440 recently. the program is dead when execute the "bl lowlevel_init" in start.S, even i put the "bl lowlevel_init" in the almost first line of start.S, it is dead too. it seems like something wrong with the label "lowlevel_init", but "bl red_LED_on" works fine. can anybody tell me why? this is all i use: Compile: arm-linux-gcc-4.3.2, arm2440 develop board, u-boot:2009.06

thanks and sorry about my english!