Snmp - Switch discovery

Hi Guys
I am currently testing your Service Desk Plus software.
Great software.
The only issue I have is that I cant retrieve any information from switches.
I'm not sure if its possible with this product.

I am recieving an RPC error and i would have thought it would use SNPM withthe public string.

Hope you can help as its the thing I cant do with service desk.

Many thanks

Grege