Hello,
This is normal, every value is counted for the maximum NMAX=300, and your number of culverts is the reason, it is still OK for the abscissae but them you go beyond 300 with the ordinates. You can try to recompile after changing NMAX in lecdon_telemac2d AND the equivalent in homere_telemac2d. In version 6.3 this number is now declared once in declarations_telemac2d.f, as MAXKEY, and it is equal to 400, so it would have worked.
With best regards,
Jean-Michel Hervouet