If you get NETFILE error code 51 it means there are invalid characters in the City name that you entered as part of your tax return's street address. To fix this:

TurboTax Online

1. Using TurboTax Online, from 2024 tax return, select Personal info > Edit.
2. At Your personal info summary, at Contact info select Edit.
3. At Let's get your contact info, in the Street address field, under What's your mailing address, look for the invalid character(s) and remove them, then select Continue.