The good old disappearing XML service. I've had this on Citrix servers before, everything seems fine but its just not talking (the event log isn't even very helpful), scan through the services and where's the XML service? its simply not there, run "ctxxmls /R88" to register it on an unused port and whew! its all working again - (also just a little edit in Web Interface)
Its actually quite busy, we have Web Interface on 80, the STA also using 80 on IIS, the controllers posting for the workstations on 8080, the XML service on 88 (although this could arguably share with IIS), tomcat running the licensing on 27000, and Secure Gateway on 443.