Most probably you added your web service as a web reference instead of a service reference. When using this type of references with wcf services, sometimes you find that your service methods change from
mymethod(string param1, bool param2)
to
mymethod(string param1, bool param2, bool hasParam2)
Or something very similar. Right? Just remove the reference and add it again as a service reference.
In case you did that to spare web.config changes and endpoints, just remember changing the url property of your service in other enviroments. Because is hardcoded in the reference and you may not know it!