Once you are locked from Netfiling, you will not be able to unlock the return, you will have to start a new return.
The error might have occurred because you started preparing the returns of the spouses together. When you choose the status of your daughter as married, in the next screens you will be asked if you want t to prepare the return together or separately? Since her husband does not have a SIN number and will not be filing a tax return, your answer should be "separately". You should not choose "filing together" then add zeros for the husband's SIN number on his return.
If you still have issues after following this process, please contact our support line:
I hope this was helpful