According to my network diagram, There's a RB750GL with 3 active Ethernet ports

Ether1: connected to a SXT5HND on it's Ethernet port, through a layer2 switch.
Ether4: connected to a 3com layer2 switch
Ether5: connected to a cisco router as gateway for intranet (which connected to a iDirect satellite router and etc...

All of those ports are in a same bridge which running Spanning tree as protocol mode.
There's a VLAN with id 1010 on Ether1 and same on Sxt's Ether1 to separate my Internet line.

the IP address of this VLAN is 192.168.10.0/24 and 192.168.10.254/24 on SXT - 192.168.10.253/24 on RB750GL both on VLAN.
These devices can't ping each other in L3 (Why? ), but ARP ping or MAC ping are working well!

Both ARP tables is native and have each other IP address and MAC address. there's no firewall filter rules too.

(ROS 6.4 with latest routerboard firmware on both).

I got suspected to the switch CAM table which between SXT and 750GL, changing the IP address range from 192.168.10.0/24 to 172.16.255.248/29 (because wasn't access to restart switch physically!) solved the problem