keil for arm,/target not created

in mdk305
when i build target
it report the error:
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build target 'lpc2106'

assembling startup.s...

/cygdrive/c/cygnus/arm-tools/bin/../lib/gcc-lib/arm-thunb-elf/3.3.1/../../../../arm-thumb-elf/bin/ld: warning:cannot find entry symbol _startï¼›defaulting to 00008000

startup.o(.text+0x12c):/cygdrive/d/allwork/keil/startup.s:400:undefined reference to '_start'

startup.o(.text+0x12c):/cygdrive/d/allwork/keil/startup.s:400:undefined reference to '_data'

collect2: ld returned 1 exit status

target not created
*******************************************************
what does it mean?and how to resolve it

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