web service not error browsable

Hi There,
 
I getting an issue when I try to browse me webservice. I keep getting the error "Cannot serialize interface System.Collections.Generic.IEnumerable" when I try to browse the published webservice. How can I get around this?

I'm using a Linq query to return a generic list.
 
 public IEnumerable<Products> GetNextForSlideshow(string mylistItem,int cnter)
        {
} 
Sean 
 
 
...