Citrix Web Interface 5.4: Error occurred while making the requested connection

I recently ran into a bizarre issue with users not being able to launch applications from a very old Citrix Presentation Server 4.0 farm when trying to launch from Citrix Web Interface 5.4. They were getting the eminently unhelpful, “An error occurred while making the requested connection.”

In the web interface application logs, I noticed this:

An error of type IMA with an error ID of 0x80000003 was reported from the Citrix XML Service at address (servername)

And this:

The farm MyFarm 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.

To resolve this, I modified C:\inetpub\wwwroot\Citrix\XenApp\conf\WebInterface.conf on the Web Interface servers and changed the RequireLaunchReference directive as follows:
RequireLaunchReference=Off
(It was set to On)

And it worked. Supposedly, that directive must be set to Off when using Web Interface 5.4 with PS 4.0. But, I’ve been running for years with it set to On and it worked fine until recently. Another Citrix mystery.

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