GS324 - Connection between two PCs appears on arp -a but fails to ping.

Dear all,

Previously to purchasing the Netgear GS324, I was using a ZYXEL GS1200-5 managed switch to connect 4 PCs together. I had manually assigned them ip addresses and they could all ping each other happily.

Most notably I had my main PC set to 192.168.1.99 and another at 192.168.1.104.

Now whilst trying to switch over the the GS324, I am no longer able to ping between these two PCs. Interestingly all other connections still work, however my 104 PC cannot ping to any. when running arp -a, I can see the 104 ip address, but then I ping and it fails and then i can no longer see 104 after running arp -a.

The final intrigue is when i restart the netgear, I can ping no problem for the first 2 seconds and then it starts failing.

Any advice for why this may be would be greatly appreciated.