Attach service to service provider

Hi again still struggling with this I really need to get it fixed . Help please...
I am trying to attach a service to a service provider . I select the provider tick the box select the service , then I go to save service provider and I get this message
* You must select at least one service, otherwise provider will not be saved!
No service providers defined

I am pretty sure my service providers are defined - but me being me who knows? Can you help please.