Cannot serialize interface System.Collections.Generic.IDictionary

What does this mean? google search turns up nothing.

The curious thing is that I get this message when I try to access the web service directly in the browser http://localhost/Myservice/Service.asmx

But when I use the service (I invoke it 开发者_开发百科inside my Jquery code) it works perfectly. Very curious detail....

This might be because you have a function in your web service that returns an interface, or that returns an object that contains a property or function using an interface. For further details on interfaces and serialization take a look at this SO question.
When you use your web service from javascript you only call one or more specific functions, but browsing on your web service with internet explorer forces a request of a whole wsdl description of your the web service with all its functions. I guess that is why it worked for the first case and not for the second.