Captcha problem / “suspicious activity”

A member of a forum I run cannot log in to post or view the hidden boards. I’m certain this is the only forum with which he’s registered on forumotion and that he is not a spammer/hacker/scammer, etc…
 
This is what he sees when he tries to log in:
https://www.youtube.com/watch?v=RUA8QyQRba8&feature=youtu.be
 
My French is pretty terrible, but I guess the message reads that the suspicious activity on his account cannot be resolved through the captcha alone, even though he entered it correctly, and that support should be contacted. The support link appears to redirect here, so I hope I've posted in the correct place.
 
I’ve put his account email behind a spoiler. I doubt he can even register here to report the problem due to this restriction, although I could persuade him to do this if this is required.

spoiler:

 
Please advise what course of action should be taken. Thanks.

Salut mon frère
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Hi @offdutytrip,

Is this the member's account ?
http://highspirits.forumotion.com/u24

I saw on the memberlist they've logged in recently, has the problem been resolved ?

Hi.

I deleted their account and they re-registered. Seems they can now log-in and post normally.

I'll mark the topic as 'solved' even though this fix isn't ideal. Would still be a problem if someone had made a lot of posts, for example.