Hello @user652892 ,
When and where are you seeing this error? I went to schedule your email to see if I could recreate what you're describing, and it scheduled without any issues. Did you resolve the issue after posting this?
Hello @JeanC245. I see you chatted with our support team this morning regarding the error. It looks like you were able to create a welcome series that allowed you to schedule the email. I brought the error up to our upper level of support and they're going to review this further.