Already activated ':c

"The product code you've entered has already been activated by a different Steam account. This code cannot be used again. Please contact the retailer or online seller where the code was purchased for assistance."

Duplicate key.

Same here. Steam sais is a duplicate key.

Thanks. Activation worked fine.

666lhdkiller, PeterIntelligence, smilickaf - Check the new key

like others here,
"The product code has been activated by a different Steam account. This code can not be used again.
☹