Attempting to launch a Citrix XenApp / XenDesktop 7.x application published with a NetScaler VPX fails with: “Unable to launch your application. Contact your help desk with the following information: Cannot connect to the Citrix XenApp server. Network issues are preventing your connection. Please try again. If the problem persists, please call your help desk.”

Problem

You attempt to launch a Citrix XenApp / XenDesktop 7.x application published with a NetScaler VPX:

The following Citrix Receiver Remote Desktop Connection window is presented and displays the progress bar:

Starting…

More information

Clicking on the More information button displays:

Connection in progress…

Less information

The progress bar does not proceed any further and the process eventually fails with the message:

Unable to launch your application. Contact your help desk with the following information:

Cannot connect to the Citrix XenApp server. Network issues are preventing your connection. Please try again. If the problem persists, please call your help desk.

Attempting to launch the XenApp desktop displays the launch window:

… but will fail with:

The connection to “XenApp Weir Desktop” failed with status (Unknown client error 1110).

Solution

While there could be several reasons why this error would be thrown, one of the possible causes is if the Citrix session reliability port 2598 is blocked from NetScaler to application server.  Ensure that the NetScaler can access the XenApp server via TCP port 2598.