I have a web service which is exposed to a web app.
The service accepts an object of type Billing.Check as a parameter.
The web app creates an instance of type Billing.Check.

The problem is I get the following error:

cannot convert from 'ClassLibrary1.Class1' to 'WebApplication1.myWebRef.Class1' 

I'm confused as both the service and application are referencing the same assembly for the type Billing.Check.

Any ideas?

Normally, the service would have the definitions for Billing.Check, when you create a proxy for the service in your client web app, you would need to use that proxy lets say localhost, to create an instance of the Object Check. Example localhost.Check myCheckObj = new localhost.Check();

IF you could provide more code and where exactly you are seeing the error, it will help to track the problem.