About F5 LTM some question

Hello all,

My structure is as follows 

All gateway is on Core SW.
F5 LTM have SNAT.

Clients must log in to the F5 web server with an AD account and password for load balancing.Why I always get a validation error on F5's Self_IP when I log in with AD account and password?

Is path is  " Client -> F5 LTM -> Web Server -> AD " ?

Do I need to do any additional setup for F5 ?

Any Help is appreciate.