static ip works dhcp Assigned IP not work

environment:

1. D-link 7100 router provide internet service. DHCP enabled from 192.168.0.140 to 192.168.0.240

2. A DC setup to provide DNS and DHCP, server IP192.168.0.10. DHCP enabled from 192.168.0.20 to 192.168.0.100

3. a normal switch connect the router and DC. 

3. Client by default will get IP from DHCP (DC server) .

problem:

some computer got the IP from DHCP server but can't ping through the router, but if you change to manual Ip address it will work, or after restart the router also works. 

so any ideas? thanks a lot. 

Misnotm