If you are using a preloader and it works on the root site but does not work on a subsite, you need to activate the Publishing Feature on your subsite. Please follow these steps:
1) From any page within the subsite, click Settings and then click Site settings.
2) Under Site Actions please click Manage Site Features.
3) Scroll down to find Share Point Server Publishing. On the right, click Activate.
This will enable the preloader settings on your subsite.
Please contact us in case you have any questions or suggestions.
Thank you for your attention!