Issue sending e-mail

On a form we created to register new members in our scouts group we send a few e-mails based on form data. Based on certain values in a field I want to send a different e-mail to the parents of the child. This however does not seem to work. How this is setup:
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- Parent fils a field (drop-down box)
- In the actions section a group is created based on the variable that is filled
- The group is devised in two sections, each for the different e-mail. Based on the group flow the e-mail should be send.
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However when debugging this I get the messageL
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​

    [email_nieuw] => Array
        (
            [recipients] => Array
                (
                    [0] => << based on e-mail variable >>
                    [1] => 
                )

            [subject] => Succesvolle nieuwe inschrijving voor Bram
            [body] => <<<<data omitted>>>>
            [from_name] => Scouting Sint Patrick
            [from_email] => << omitted >>
            [reply_name] => Verenigingsbestuur scouting Sint Patrick
            [reply_email] => << omitted >>
            [result] => the Mail could not be sent.
            [var] => false
        )

​
This does give me the information that the mail is not sent, but I cannot find out how and why this error is orruring. Please see the form backup attached. Hope someone can help me...

Hi scoutingsintpatrick,
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This looks OK apart from the empty entry in the recipients array, I guess that might cause a problem.
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Your backup form is not attached (I think that there is a problem on the site here with attachments). You can PM me with the site details if you like.
​
Bob

hi bob, the empty field is because only one contact was filled (of 2 possible contacts) this setup was the same in V6 and there it worked. I can send you the form in a pm later.