Answer
Each ArcPad registration code is valid for use on one Windows installation, and one Windows Mobile device installation, with the registration code residing in the local user registry (HKEY_Current_User) rather than the local machine (HKEY_Local_Machine).
Thus, multiple users using the same device but with different user accounts must enter the registration code at least once to access ArcPad on the same device. If a registration code is not entered in ArcPad upon initialization, the user is able to access ArcPad for 20 minutes before it is required to be restarted.
Note:
Administrative privileges are required to enable the user to enter the registration code.
This is a known bug. Please review bug NIM074863 for the latest information on this issue.