Criteria to use 'login access' in a subscriber organization

The following circumstances will prevent a user from granting login to a package: 

• A system administrator disabled the ability for non-administrators to grant access.
• The user doesn’t have a license for the package.
• The package is licensed to the entire organization. Only administrators with the “Manage Users” permission enabled on their profile can grant access.
• The organization preference Administrators Can Log in as Any User is enabled.

Note: Unless the organization preference Administrators Can Log in as Any User is enabled, access is granted for a limited amount of time, and the subscriber can revoke access at any time. Any changes you make while logged in as a subscriber are logged in the audit trail.