Code: 96 General Failure

[Helgaiden]

My girlfriend's Moment has started having issues sending text messags.Sometimes when she attempts to send a msg it gives a Code: 96 error and doesnt send so she retries multiple times and then sometimes it eventually sends through those multiple times and the person receiving get the txt like 5 times. What is this error and how do i fix it? Its using the stock messaging app.