I have two PCs as two different networks… and a mikrotik router rb450…
PC-1 ==> IP = 192.168.90.2/24 and gateway 192.168.90.1 (the router interface, connected to the PC)
PC-2 ==> IP = 192.168.91.2/24 and gateway 192.168.91.1 (the router interface, connected to the PC)
Router has, on ethernet1==> IP=192.168.90.1/24 and on ethernet2==> IP=192.168.91.1/24
I can ping from one PC to router’s other interface which is connected to another PC, bt still i m not able to ping from one PC to another.
When I Tracert from PC1 to PC2 , I receive replies from PC2’s gateway (the router interface, connected to the PC2).
To solve this, I have added the following routes also :
1)destination=192.168.90.0/24 with gateway=192.168.91.1
2) destination=192.168.91.0/24 with gateway=192.168.90.1
Also tried disabling the firewalls on both the PCs…
but nothing helped… 
I m not getting, What could be the problem… plz help me…