Samsung tablet keeps asking to allow data access when plugging to PC by USB
This is a workaround more than a fix, but it works for me on another Samsung device. 

Install Samsung SideSync app from the Google play store on your device, then install Samsung SideSync app on your PC (http://www.samsung.com/sidesync). 

After one more "allow access" popup, it won't ask again as the SideSync app will keep the allow access permission open.