Reproduction steps:

1. Navigate to "<Drive Letter>:\Users\<Name>\AppData\Roaming\Unity\"
2. Right click on "Packages" folder and open properties
3. Open "Security" tab
4. Click "edit"
5. Select your Windows user account in "Group or user names" list
6. Put the checkbox in the row "Full control" and column "Deny" in the "Permissions for <...>" list
7. Click "Apply"

Expected: Unity launches
Actual: Unity home screen opens, but is blank -OR- "Copying file failed" error window appears

Also, if the error window appears, clicking on any available button will throw the same error just about another file (see the attached Editor.log file). After all error windows are closed, it proceeds to the blank Unity home screen.

Reproduced on: 5.5.4f1, 5.6.1f1, 2017.1.0f3, 2017.2.0b2