Thank you ..
The problem was: (1) I had an input inside a structure with a line out to a later structure - fixed that by placing the first input also outside the structure, with a string into both the earlier and the later structures where that data was needed. (2) Apparently I had some old inputs to the concatenate string vi which had not been fully erased - one of the errors said I had multiple inputs, although one or two of the old inputs were not visible on the diagram; apparently the concatenate strings.vi knew about them. With these fixed, it runs fine, records date and time, plus which board is being interrogated, and which port, then the data from that port is recorded to disk continuously.
Thank you for your help.
Dave