Can't invite more than one user on wiki

We can't invit a user to a wiki, you can check the issue by the following steps :
1- Go to the section Administration > user
2- Select a user and click on invite ( Screen : invit-user.png )
3- The user will be invited to the wiki
4- Select another user and click on invite, you'll see the following message :
" Nom User a déjà une demande en attente. Veuillez répondre à cette demande de rejoindre." ( Screen : error-invitation )