Här är lösningen som brukar fungera:

1. Unlink the OneDrive Next Generation Sync Client.

2. Exit all Office applications.
3. Go to Control Panel > User Accounts > Credential Manager > Windows Credentials.
4. Remove all credentials there(This will remove your stored passwords.).
5. Run regedit as an administrator to open Registry Editor.
6. From Registry Editor,

for Office 2016, browse to:HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities.

for Office 2013, browse toHKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity\Identities.
7. Check to see if there are any folders listed under Identities. If yes, delete them.

8. Running C:\Users\UserAccountName\AppData\Local\Microsoft\OneDrive\OneDrive.exe /reset in the command prompt to reset the OneDrive Next Generation Sync Client.

Note: the user account is the log-in account for your computer.

9. Clear IE caches via Tools>Safety>Deleting browser history , reset IE and restart the OneDrive Next Generation Sync Client to sync files.

Stulet ifrån: http://answers.microsoft.com/en-us/msoffice/forum/msoffice_word-mso_win10/upload-failed-you-are-required-to-sign-in-to/b9b9b4a0-4d68-4d9e-b393-82ae3192c805?auth=1