When I tried NetFile I got error message saying it is not first time I have filed a return and I need to change that in the software. Where do I change that setting?

Please return to My Info > Taxpayer's Personal Information > answer NO to the question "Are you filing an income tax return with the CRA for the first time?". Then return to the File section and attempt to NetFile your return again.

If you are unsuccessful again, then you should contact CRA @ 1-800-959-8281