"Zen Cart 1.3.9a Users: upload everything inside the admin folder to where ever your admin folder is on your server, and that's it... you're finished!" (v1.01)
For 1.3.9b:
This should be corrected to upload only "twitter" folder on admin. The update_product.php has somehow commented out line 198 (don't know if this is intentional) but it resulted in getting a screen of the category without the controls after one inserts a product.
see pic on this forum post:
http://www.zen-cart.com/forum/showth...412#post884412