You mentioned it was 4 flights. I am not sure how long ago the flights
were, but if I recall there is a 24hr or 48hr window as to when you
can post your flight. If you are outside that window, I dont believe
it accepts it any more.

I wouldnt discard the theory of needing your logger ID though. I have
seen that work many times, and others it seems that any file "name"
will be accepted. The logger ID is a part of the data that comes along
with the igc file (At least in the loggers that I have looked at) so I
am not sure if the validation code is looking at the file "name" or
the data.

I hope you get it working!