Legacy Citrix apps not launching on newer Web Interface servers

If you ever try adding a legacy Citrix Presentation Server 4.0 farm to a Web Interface and the apps don't launch, check the application event log on your Web Interface servers for Error 31203 messages like below:

`Source: Citrix Web Interface Event ID: 31203 The farm XXXXX has been configured to use launch references, but a

launch reference was not received from the Citrix XML Service.

Check that the farm supports launch references or disable launch

reference requests. [Unique Log ID: XXXXXXX]`

Launch references are only support with Presentation Server 4.5 and above. To fix this, go to your WebInterface.conf on your Web Interface servers:

C:\inetpub\wwwroot\Citrix\XenApp\conf\WebInterface.conf

and change RequireLaunchReference and OverrideIcaClientname to Off and On respectively:

RequireLaunchReference=Off OverrideIcaClientname=On

Update September 4, 2012:

I was informed by our Citrix SE this issue impacts Storefront as well. The work around above will work by changing the same settings in the web.config of the Storefront site.