Denis K

SOLUTION:
The solution posted in John Wiernikowski's post above worked both for mine and my relative's 2021 UFile Online tax files. John, thank you for posting, even though that solution didn't work for you. Hope you get it solved.
Here are the exact steps I took:
1) Delete the 2021 tax file
2) Open the 2020 tax file. Go to tab 4 (Tax return)
3) Download the 2020 tax return in PDF
4) Click "Settings" in top right corner, click "save & close"
5) Create the 2021 tax file. Wait for it to load for a minute or so.
6) Click "start new" file.
All personal data, dependants, carry forward amounts were rolled forward.

No. You have to do it manually.

I ran into this same issue just now and tried the hotspot technique -- that didn't work. What solved it for me was adjusting the time and time zone properly on Windows. For some reason Windows often comes up with the wrong time-zone, hence the local time is incorrect. If the inaccurate local adjusted time is used in various cryptography algorithms, the negotiation with the CRA servers will fail. 
For me, I just right-clicked the time/date in the status bar, forced a sync with the time server and forced a sync of the time-zone. CRA download then worked perfectly.
Hope this helps others.

Actually we helped one client that had a similar issue and succeeded by changing internet provider. Essentially, she used her phone as hotspot to connect to the internet and then returned to her regular ISP and everything worked. If you need help please reach out to our support dept.  ASAP. 

George Hiotis QA Manager UFile.ca 

Hi,
(*) To run UFile for Windows, your system must meet the following requirements:
Operating system: Windows® 8.1, Windows® 10 or Windows® 11. Hard disk space: 250mb available. Display: Screen resolution of 1024x768 or greater. Internet access: is required in order to use NETFILE / EFILE, and obtain the latest software updates. If not, I suggest to try our UFile ONLINE product which works on any OS.
UFile ONLINE | Tax Software for Canadians. Get the best tax refund.
Thank you.

Hi @FionaH,
You can add your dependant to your file to claim the eligible credits and only transmit your return within that file and then create a new file for your dependant as a family head to have her own different address but you cannot change your mailing address using NETFILE. Any changes to your mailing address will not be updated with your return. CRA will use the mailing address they already have on record for you. You must contact CRA to change your mailing address prior to NETFILE.
Thank you,

Hi @VIJAYKUMAR DAVE,
Before filing any return as a professional, the client must sign the T183 for Federal and the TP-1000 for Quebec. These forms are generated automatically upon an eligible return under the Tax return tab.
If you wish to have a client letter, then you can look at our DTMax product:
https://www.thomsonreuters.ca/en/dtprofessionalsuite/products/dtmax/dtmaxt1.html
Thank you,

Perhaps UFILE should indicate that an update is necessary before one can Netfile.
Tax completed - no errors - but cannot Netfile. Tell us why and indicate update may be necessary. Thanks.

Day traders usually report their gains as business income. For instance
https://fbc.ca/blog/calculating-taxes-when-day-trading-canada/
https://www.daytrading.com/taxes/canada

If you are looking for the T777s, it's in Employment and other benefits.

Downloaded the 7zip file.  Right clicked on downloaded UFile icon and selected the 7zip command to get to five files in the downloaded file.  clicked on the .exe file.  Surprise!  Surprise!  It installed!