One Subnet or Two?

Network with 2 Subnet: 192.168.0.0,192.168.10.0.
about 300 workstations
A linux Server act as a Gateway.One NIC with binded with 2 IPs(192.168.0.250,192.168.10.250)
We have this problem now:
when some workstations try to open files on servers which is located on another subnet,sometimes error occurs(fail to open word,access files)

Now,I suggest two solutions:
1.Add another NIC on the Linux Gateway.
2.Use 255.255.254.0 netmask,and change these two subnet into one
Which is better?

Any assistance is high appreciated.