When you put the condition if as invariant, "server" application throw the
exception, while Uppaal has to report syntax/semantical problem.
Any keyword in an invariant seem to cause a server crash. This is most likely a problem in libutap.
Fixed on the trunk. The problem was caused by any kind of syntax error (but not
type error) in an invariant when reading an XML file (the GUI uploads the model
as an XML file).