I had the absolute worst tech support call ever with TurboTax technical support.
After changing the environment variable didn't work for me I gave them a call.
I was on the phone for over an hour and the guy was completely clueless. He acted like he was searching Google as I had been.
After giving up with him I checked the Event Viewer and found the following error:
"Product: TurboTax 2021 -- Error 1305. Error reading from file C:\Users\[USERNAME]\AppData\Local\Downloaded Installations\{98531A59-92D1-40BA-AD49-466E08FEB552}\TurboTax 2021.msi."
Error 1305 leads to permissions.
By default, almost all system files, system folders, and even Registry keys in Windows 10 are owned by a special built-in user account called "TrustedInstaller". I thought I'd try resetting permissions.
By opening an elevated command prompt and typing icacls "full path to the folder" /reset /t /c /l
This fixed my issue completely.
