If you , try Adobe’s “Find your serial number” tool or check your Adobe account. If you don’t have a valid license CS6 is no longer sold, but using cracked keygens or offline response generators is piracy. Error 99 is a sign that those tools don’t work anymore for CS6 — because modern offline activation checkers have been patched in the last CS6 updates (version 13.0.x).
No legitimate offline activation process yields error 99 when done correctly with a genuine serial and Adobe-provided response.
It sounds like you’re running into (or “response 99”) when trying to offline activate Adobe Photoshop CS6.