First of all, WTOS 6.5 does not support network traces. This is a features that was introduced later. What you are donig is tracing an ICA or RDP connection. This means that you a creating kind of a movie of your session which can be played back later to show some certain behaviour.
If you need a real network trace you would have to use some 3rd party tool like MS Netmon, Etherreal or similar.
Check your FTP log to find out why WTOS is not able to create your trace.ica file.