[Solved][Q] Clockworkmod unsigned? Won't install.

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I've just tried installing CWM on JPO (From samfirmware.com)
It doesn't work, it says when trying to flash it (from ROM Manager)

Update media, please wait

update media, finished

-- Install from package...
Finding update package...
Verifying update package...
E:failed to verify whole-file signature
E:signature verification failed

-- Appling muti-CSC...
Installing Multi-CSC
multicsc : src /system/csc/KOR/system/ .
Installation aborted.

What does this mean and how can I fix it?

Thanks,
Luke.

Anyone? Surely someone knows what this means.

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