The error message "Device ID # is assigned to a different user" indicates that a PC has already been locked to another user of FieldAgent™ Desktop.  FieldAgent™ Desktop locks a single FieldAgent™ account to a single Windows user in order to ensure data privacy.

To unlock a Windows user so it can be assigned to another FieldAgent™ ID, please Support at Sentera.  

To support multiple users on a single PC, create a Microsoft Windows users for each FieldAgent™ user account.