To import upgrade packages, you must have the Upload File privilege. You can assign Update Manager privileges to different roles from the vSphere Client. For more information, see the Update Manager Privileges section of the VMware vCenter Update Manager Installation and Administration Guide.
After updating the permission, ensure to logout and login again to vCenter Server using VI Client and then try to import the ESX/ESXi 4.1 upgrade package.
Based on VMware KB 1024394