splog request captcha not working on 'anti-splog' plugin

Hi there,

I am running a WP multisite network protected by the 'anti-splog' plugin but some customers reported that when their blog was automatically marked and blocked as splog, the captcha displayed on the request page was impossible to solve.

And in fact, I tried to solve one and didn't succeed neither.

Do you know what could cause this problem ?

Or is there a way to simply disable the use of a captcha for this page ?