CAPTCHA does not currently work if you are using a Reverse proxy cache such as Varnish. See #562374: Mollom incompatible with Pressflow's (and Drupal 7's) session handling -- causes CAPTCHAs to fail.

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soxofaan’s picture

soxofaan commented
Status: Active » Closed (duplicate)

Thanks for the interesting link.
This is clearly a duplicate of #632742: Caching with Boost, Varnish, ... causes "CAPTCHA validation error: unknown CAPTCHA session ID"

q0rban’s picture

q0rban commented

Hmm, not sure how I missed that, thanks!