The problem was that the LADATE variable was actually a call-by-reference argument (FORTRAN77 default passing convention):
SUBROUTINE MDATE(LADATE)
character*20 date_char
character*10 LADATE
...
write(LADATE,"(2A2,A4)")
S date_char(3:4),date_char(7:8),date_char(9:12)
RETURN
END
and it was passed as an argument several subroutines above as a just an 8-character string. Simply written, the call would be equivalent to:
...
CHARACTER VAR*20
...
CALL MDATE(VAR(10:17))
...
The program started, but after an attempt to access an inaccessible array addresses by the write function the breakpoint was triggered.