Service reference class isn't recognized

Question

I have added a service reference that has the class ServiceSoapClient that I can use as in the example, and it is recognized before the code is executed:

Public Shared Function NewClient() As ServiceSoapClient
...
End Function

Partial Public Class ServiceSoapClient
        Inherits System.ServiceModel.ClientBase(Of Something.ServiceSoap)
        Implements Something.ServiceSoap
...
End Class

Now, during execution I have the above error on the page:

Compilation Error

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: BC30002: Type 'ServiceSoapClient' is not defined.

Source Error:

...
Line 5:          Public Shared Function NewClient() As ServiceSoapClient
...

I don't understand how is this possible, do someone has an idea. Thanks in advance.