Unable to Connect to Silverlight Application


You cannot record your Silverlight application through Test Studio and receive an "Unable to connect" error message.


  • The MIME Type for your XAP file is not properly registered on your web server. This is the most common cause for this type of issue.

  • Automation only supports .XAP Silverlight app deployment (the .NET method).

.XBAP or Javascript Silverlight deployment is not supported.


1.  Make sure that you have registered the .XAP file extension within IIS. These instructions are also documented here.

a. Click Start > Run (XP) or Start then click in the search field (Vista/Win7/Win8). b. Type IIS within the search/run field. c. Hit 'Enter' on your keyboard. d. Make sure you are targeting the "Default Web Site" in the left column. e. Double-click MIME Types in Features View. f. Click Add (right column). g. Set the file extension to .XAP. h. Set the MIME Type to application/x-silverlight-app i. Click OK.

2.  If the Web and Silverlight app is deployed locally, try adding a period ('.') after localhost, as in http://localhost.:

3.  Delete the entire cache for the test playback browser:

a. In Interent Explorer, select: Tools > Internet Options > General Tab > Delete (Within the browsing history section)

b. In Firefox, select: Tools > Clear Recent History > Select Everything in the 'Time Range to Clear' drop-down menu > Choose Clear Now

c. In Safari, select: Settings (the gear in the upper-right of the Safari window) > Reset Safari > Check only Empty the Cache > Click Reset

d. In Chrome, select: Tools menu > Options > Click the Under the Hood tab > Click Clear browsing data...

4.  Reset Internet Explorer settings.

5.  Try increasing the (Settings.) Silverlight Connect Timeout if the Silverlight app has a longer load time.

6.  Try setting externalAccessfromCrossDomainCallers to script only your application's AppManifest.xaml file by doing the following in your html page and Silverlight manifest:

a. Example for html page:

<div id="silverlightControlHost" />
<object height="300" width="300" type="application/x-silverlight-2" data="data:application/x-silverlight-2," >
<param value="http://a-remote-domain.com/ClientBin/SilverlightClient.xap" name="source" />
<param value="white" name="background" />
<param value="3.0.40723.0" name="minRuntimeVersion" />
<param value="true" name="enableHtmlAccess" />
<param value="visOnly=true" name="initParams" />
<a style="text-decoration: none;" href="http://go.microsoft.com/fwlink/?LinkID=149156">
<img style="border-style: none; width: 400px; height: 200px;" alt="Install Microsoft Silverlight" src="http://storage.timheuer.com/sl4wp-ph.png"/></a></object>
<iframe style="border: 0px none ; visibility: hidden; height: 0pt; width: 0pt;" /></div>

b. Example for SL Manifest:

<Deployment xmlns="http://schemas.microsoft.com/client/2007/deployment" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" ExternalCallersFromCrossDomain="ScriptableOnly">

See this Microsoft forum thread for more information

7.  Try setting the "windowless" property for your Silverlight app to "true":

Example (similar to first example above):

<object id="xamlHost0" width="900" height="412" type="application/x-silverlight">
<param value="transparent" name="background"/>
<param value="true" name="windowless"/>
<!-- a bunch of other params go here -->

8.  Check the headers your server is sending for the Silverlight Page by:

a. Install/Run Fiddler and load your Silverlight page.

b. Click the response for the .xap file

c. Click Inspectors > Headers.

There should be an entry titled: Content:application/x-silverlight-app This must be in response in order for the Telerik Testing Framework or Test Studio to detect the Silverlight app.