No access?

[cska133]

@Bennor

If you have already accessed a Private Share using one set of credentials (like Admin) and are now trying to access a second Private Share using a different set of credentials (test) chances are you’ll run into a problem with Windows. There is a known issue where certain versions of Windows won’t allow the user to use two or more login credentials when accessing NAS devices like the My Cloud. The workaround is to unmap all Shares that are mapped. Remove any My Cloud credentials in the Windows Credentials Manager, reboot the computer and try using the different set of My Cloud credentials.

just for the records if other user (Windows7) have that issue:
Go into the Control Panel (Systemsteuerung) → User accounts (Benutzerkonten) → Windows Credentials Manager (Anmeldeinformationsverwaltung).
There will see your My Cloud device and its saved credentials (username and password). You can modify or remove them.