Unable to change user group
 

I have two members who are awaiting moderation for registration. When I go into the Admincp and find them I change their group status (one at a time) to 'registered' instead of 'awaiting moderation' and the system refuses to change the group and throws up this message:

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I've checked the admin permissions and excluding a few options that need to be 'no' everything else is set to yes, but I cannot change the user group which means these members cannot use the forum. Any ideas?
Attached Images

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