I have had the same problem. After trying all but uninstalling/reinstalling to no avail. I cleared all Windows Temp Files, Chrome and Edge cookies and history, and still got Error 70001. In Win10 Task Manager, TurboTax.exe wasn't shown in the Processes list. Under the Details tab, it showed as Suspended with UAC virtualization Disabled, running under the desktop user account in which I was logged in. Couldn't stop the program from there: "Access denied" (even for the Local Administrator).
What finally worked was this:
1. Log in with a Win 10 Local Administrator account.
2. Rename "C:\Program Files (x86)\TurboTax\Individual 2021\32bit\TurboTax.exe" to "C:\Program Files (x86)\TurboTax\Individual 2021\32bit\TurboTax-yymmdd.exe", where "yymmdd" is the current date (so you'll know when this was done).
3. Shut down and re-boot your computer. On startup Win10 can't launch TurboTax.exe (it's not in the Win10 Startup apps list but it launched anyway when the program file was named TurboTax.exe).
4. Rename "C:\Program Files (x86)\TurboTax\Individual 2021\32bit\TurboTax-yymmdd.exe" to "C:\Program Files (x86)\TurboTax\Individual 2021\32bit\TurboTax.exe".
Then I could open an run Turbo Tax.
Some thoughts.
I had this problem after leaving TurboTax via File-Save-Exit to have dinner. Win10 went into sleep mode while I did that. Got Error 70001 when I tried to open it to finish after waking up Win10. That time, shut down and reboot fixed that. I finished entering and checking my return at 2:00am. I used File-Save-Exit to close TurboTax and I put Win10 into sleep mode. Next morning after shaking Win10 awake, Error 70001 persisted even after power off on computer, router, cable modem. After calling Support and having a productive conversation, I tried the file-rename-reboot-rename trick and it worked. It's quicker than uninstall, reinstall, re-update and it seems to work. You might have to do this every time your computer sleeps? I didn't try a shutdown/restart instead of a sleep/wakeup cycle so that's an unexplored possible workaround.
Intuit really should investigate this issue more thoroughly and pinpoint and fix the code that causes this aggravation. As it is, a late-to-prepare taxpayer could miss the filing deadline.
