DLink to CISCO switches over fibre

[Trapper]

Hi Folks,

 

I have a core DLink Web Smart switch connected via fibre to three CISCO switches on site.

 

The fibre is TX and RXing traffic (lights flash, logs say packets are moving) however client machines cannot access any network resources off their switch (e.g. although the fibre is sending and receiving data, it isn't actually doing anything useful).

 

Any ideas?!