Help! Error configuring Tenor a800

Hi,

I am trying to configure a tenor a800.
I have static IP(DSL) from my ISP.
When I am trying to assign an IP address and the subnet mask it does not accept them, I get a message that says “Invalid IP”
But I tried assigning the same IP and subnet mask to a PC and it works fine.Any ideas what could be causing this. I am stuck at this stage.

Any help would be greatly appreciated.

Thanks!