Client "launch file" error

I’m getting the following error when attempting to launch Client:

"An error occurred while launching/running the application.

Title: Servoy Client
Vendor: Servoy
Category: Launch File Error

The following required field is missing from the launch file: (|||)"

I’m on a Mac, connecting to a Windows server running 2.2.1rc3 (but it has been happening since at least rc2). Both machines have Java 1.5.
I’ve also seen this message in a Windows Citrix environment. Clearing Java caches doesn’t seem to make a difference.