asp.net web api - WebAPI and https not playing well together -

i'm getting errors (strange ones) when try get,put,post,delete https same webapi controller calls work http. there special web.config magic needed https webapi controllers?

** adding error:

(this error code when hit same web api controller 1 works http. is, http works, https fails error)

{"message":"an error has occurred.","exceptionmessage":"a null value returned instance of httpresponsemessage expected.","exceptiontype":"system.invalidoperationexception","stacktrace":"   @ system.web.http.controllers.responsemessageresultconverter.convert(httpcontrollercontext controllercontext, object actionresult)\r\n   @ system.web.http.controllers.apicontrolleractioninvoker.<>c__displayclass3.<invokeactionasync>b__1(object value)\r\n   @ system.threading.tasks.taskhelpersextensions.<>c__displayclass3b`2.<then>b__3a(task`1 t)\r\n   @ system.threading.tasks.taskhelpersextensions.thenimpl[ttask,touterresult](ttask task, func`2 continuation, cancellationtoken cancellationtoken, boolean runsynchronously)"}