ajax - SIGNALR: $.connection.hub.start() results in "Error parsing negotiate response." -

i had basic signalr functionality implemented , working in mvc5/angularjs application recently, after shelfing , unshelfing changes getting error when connection negotiated in $.connection.hub.start().

i've stripped down code basics, still error. poking around in jquery.signalr-2.2.0.js negotiate request made, found result returned ajax request http://localhost:44379/signalr/negotiate?clientprotocol=1.5&connectiondata=[] returning html of page instead of json data!

            connection._.negotiaterequest =  /* on line 659 */ signalr.transports._logic.ajax(connection, {                  url: url, // http://localhost:44379/signalr/negotiate?clientprotocol=1.5&connectiondata=%5b%5d                  error: function (error, statustext) {                      // irrelevant code removed.                  },                  success: function (result) { // here @ least...                      var res,                          keepalivedata,                          protocolerror,                          transports = [],                          supportedtransports = [];                        try {                          res = connection._parseresponse(result); // fails because result contains html.                      } catch (error) {                           // error.message "unexpected token <"  onfailed(signalr._.error(resources.errorparsingnegotiateresponse, error), connection);                          return;                      }

here javascript establishing hub/connection:

$(function () {      var hub = $.connection.testhub;      if (hub)      console.log("signalr hub initialized.");      $.connection.hub.start().done(function () {        console.log("signalr connection established.");      }).fail(function (err) {      console.log("error starting signalr connection: " + err); // ends here.    });    });

and script references (i have signalr code in separate js file named messaging.js):

  <script src="~/assets/js/signalr/jquery.signalr-2.2.0.js"></script>    <script src="~/scripts/messaging/messaging.js"></script>    <script src="~/signalr/hubs"></script>

i don't understand why ajax response signalr/negotiate returning html instead of json. i've stripped down server side hub code empty class [allowanonymous] ensure nothing in there causing problem. have app.mapsignalr() call in startup.cs in place. first thought, since occurred after shelfing , unshelfing, didn't make shelf , lost, can't seem find missing...

anyone have ideas?

i found problem while playing rules in web.config. previously, had rule signalr:

<add input="{request_uri}" matchtype="pattern" pattern="/signalr/hubs" negate="true" />

changing pattern allowed communication /signalr/negotiate, think:

<add input="{request_uri}"      matchtype="pattern"     pattern="^/(signalr)"   negate="true"/>

...i have no idea how worked before.