I have no way of knowing, but I suspect OS-10.6 may no longer support Plot flow for X.
I generally 'print' all of my output now instead of plotting.
Just a guess.
HTH's
Mark
Mark R. Wallace AIA
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MacBook 2.53 Ghz, Intel Core i5, 8 Gb,
Mac OSX (Sierra 10.12.6,
ArchiCAD 22 USA Full, +21, & 20.