Are you sure that you're not trying to activate a different version of Windows 7 (say Ultimate) with a key generated for something lesser (say Home Prem)?
If this is not it then I'm stumped. Have you tried phone activation (you don't actually speak to anyone, just pound a bunch of keys), The key on my sticker didn't work right when trying Internet activation, but did with phone activation.
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G74SX-CST1-CBIL, i7 2630QM 2GHz
32GB DDR3 RAM @1333MHz
GTX560M 3GB DDR5 (192 bit)
17.3" LED 1920x1080
Sentelic TP, BIOS 203
Debian Linux Wheezy (Testing) Kernel 3.2, NVIDIA 295.40