If you are writing an Indigo service and you can an error for something like the one shown below, then essentially you change the interface (i.e. your contract) you implemented in Indigo (now WCF), but forgot to change the interface in the web.config.

<endpoint contract\="MY-TYPE-HERE" binding\="wsHttpBinding"/>

Exception Details: System.InvalidOperationException: Could not resolve type IMyService, contract cannot be created.

Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:
[InvalidOperationException: Could not resolve type ICalculators, contract cannot be created.]