Users are unable to access the applications, and the error  "An error occurred while making the requested connection" is provided. 

The event viewer displays the following error, which indicates a licensing issue:

Source: MetaFrame
EventID: 9014
Description: The licenses required by this edition of Citrix Presentation Server are not present on the license server LicenseServerName.

XenApp 6.5 introduces a new feature to server role called License Model, which is found in the XenApp Server Role Manager console under license configuration. You can choose from the following three types of models:

• XenApp

• XenDesktop concurrent system

• XenDesktop user/device

Note: The setting to modify the License model is also possible by modifying the policies.

Selecting the appropriate license model must resolve the error. You can make these changes by using either the XenApp Server Manager Role or Policies. (Select one of the following options.)
Note: It is important to understand the meaning of Select the appropriate license model. Always select the License Model according to the License File which is uploaded.

Option 1

Perform following steps to verify software version and determine if retail version needs to be installed:

1. Check if build is a tech preview version of XenApp.
   Retail licenses are not compatible with Tech Preview versions of software.

2. To check build number, navigate to registry entry, HKLM\System\CurrentControlSet\Control\Citrix\ProductBuild.

3. If registry displays build number 6644, software installed is a Tech Preview version.
   The retails version of XenApp 6.5 must have a build of 6682.

4. If software installed is for Tech Preview, have the tech preview version of XenApp removed and install  correct retail version.

5. After correct software is installed, continue to Options 2 & 3 when appropriate.

Option 2

Perform the following steps to modify XenApp Server Manager Role:

1. Open XenApp Server Role Model.

2. Click Edit Licensing.

3. Click Next until Select Licensing Model screen appears.
   

4. Select the appropriate license model.

5. Click Apply.

6. Try and make a connection.

Option 3

Perform the following steps to Modify Policies:

1. Open App Center and navigate to Policies.
   

2. Highlight Unfiltered Policy and click Edit.
   

3. Under Categories, select Server Settings.
   

4. Click Add under the XenApp product model setting.
   

5. Select the appropriate license model.
   

6. Reboot the server.

Note: It is important to understand the meaning of Select the appropriate license model.

For example, you have purchased XenDesktop User/Device Licenses and uploaded a XenDesktop User/Device License File to the License Server. Then create the policy and select XenDesktop User Device to run XenApp Platinum as the Product, without getting the Event ID 9014 in Event logs.

Refer to following articles for more information related to Event ID 9014:

CTX123372 - License Acquisition Error 500 Occurs and Workspace Control Fails