Process cannot access file because it is being used by another process error message.
To resolve this error:
Press Ctrl + Alt + Delete, then click Task Manager.
Ensure you're on the Processes tab. Locate and right-click SidekickTrayWPF, then select End Process. If a warning window opens to ask if you want to end the process, click End Process again to confirm.
In the Start menu, search for HubSpot for Windows and open it.