Hi Malik,
Relative data path in the administrator's configuration file is NOT supported. If you, as an admin, are trying to configure startup layers for your organization, could you check if the data path specified is accessible (at least readable) by other users in your org?
Example:
<layer name="startup_tilepackage" type="TilePackage" url="D:\test.tpk" state="Invisible"/>
Thanks,
Mandy