The program has failed to trace the order outwards from the centre of the frame towards the right-hand side (increasing X).
If tracing is being attempted using a cosmic-ray-contaminated frame then the ech_decos1 option/task should be used to clean the frame prior to tracing.
The parameter TUNE_MXBADSMP sets the maximum number of failed samples allowed before the trace is deemed 'lost'.
The parameter TUNE_MXSMP determines the number of samples across the frame and thus their separation. In general, increasing TUNE_MXSMP will assist the program in tracing difficult orders.
Experimenting with the various modes of tracing set by the parameter TRACE_MODE should allow most cases to be traced.
As a last resort, the program also provides a manual trace mode in which points specified using a graphics cursor can be used as the basis for the tracing process.
Martin Clayton