Can't visit the registration page with a local version of WordPress (Japanese)

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[Environment]
Word Press Version: 3.1.2
Secure Invites: 1.2
package: Japanese (https://ja.www.ads-software.com/)
character enchoding: UTF-8
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I have installed this plugin into the local version of Word Press (Japanese),
and have following problem.

The situation is:
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1. A registerd user ‘userA’ send invitation to ‘userB’ from
Dashboard>Invite friends.

2. And userB successfully received the invitation mail.

3. But if userB click the invitation link:
https://website.com/wordpress/wp-login.php?action=register&[email protected]

userB cannot access to the registration page, otherwise,
the following message appears:
‘Sorry, you must be invited to join this community.’
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I have checked my registrations settings:
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1. Setting Presets:
‘Signup is just for invited people, and all users can invite as many people as they like’

2. settings for userA is:
– Can invite: (Cheked)
– Invitation limit: (Blank)
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But, no user who is invited by userA can reach the registoration page.

Maybe, my multi-byte character encoding (UTF-8) environment causes the problem,
but I’m not sure.

Please give me some advice.

Thanks.